• Journal of the Korean Magnetics Society
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• v.7 no.5
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• pp.237-242
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• 1997

The microstructure and soft magnetic properties of as-deposited Fe-Hf-O thin film alloys, which are produced at $P_{O2}=10%$ by rf magnetron sputtering method in $Ar+O_2$ mixed gas atmosphere, is investigated. Newly developed $Fe_{82}Hf_{3.4}O_{14.6}$ film exhibits good soft magnetic properties with $4{\pi}M_s=17.7$ kG, $H_c=0.7$ Oe and ${\mu}_{eff}$(0.5~100MHz)=2,500, respectively. The Fe-Hf-O films are composed of $\alpha$-Fe nanograins and amorphous phase with larger amounts of Hf and O elements which chemically combine each other. With increasing Hf area fraction, Hf and O contents increased proportionally. It was considered that O content in films was determined by Hf contents, because O was chemically combined with Hf. It results from decreasing the $\alpha$-Fe grain size by precipitates (Hf and O), high electrical resistivity. The $Fe_{82}Hf_{3.4}O_{14.6}$ film exhibits the quality factor (Q=$\mu$'/$\mu$") of 25 at 20 MHz. These good frequency characteristics are considered to be superior to other films already reported.o other films already reported.

• Resources Recycling
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• v.18 no.1
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• pp.38-43
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• 2009

In this study, binderless consolidation processes of ultra foe Si powder, by-products of making high purity poly-Si in the current method, were systematically investigated for use as economical solar-grade feedstock. The average diameter of the silicon powder was $7.8{\mu}m$. The main contaminants of the fine silicon powder were $SiO_2$ type oxide and humidity. The chemical pretreatment using the HF solution was observed to be effective for the improvement of the compactability of the silicon powder and the density ratio and the strength of the silicon powder compacts. The yield of the binder-free consolidation process increased by 20% under a vacuum condition. In as-received state, the silicon powder were not pure enough to be used as solar grade feed-stock material. After the dry chemical treatments, a sufficiently high purity above solar-grade was able to be achieved.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.14-15
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• 2010

Recently there has been growing interest in topological insulators or the quantum spin Hall (QSH) phase, which are insulating materials with bulk band gaps but have metallic edge states that are formed topologically and robust against any non-magnetic impurity [1]. In a three-dimensional material, the two-dimensional surface states correspond to the edge states (topological metal) and their intriguing nature in terms of electronic and spin structures have been experimentally observed in bulk Bi1-xSbx single crystals [2,3,4]. However, if we want to know the transport properties of these topological metals, high purity samples as well as very low temperature will be needed because of the contribution from bulk states or impurity effects. In a recent report, it was also shown that an intriguing coupling between the surface and bulk states will occur [5]. A simple solution to this bothersome problem is to prepare a topological metal on an ultrathin film, in which the surface-to-bulk ratio is drastically increased. Therefore in the present study, we have investigated if there is a method to make an ultrathin Bi1-xSbx film on a semiconductor substrate. From reflection high-energy electron diffraction observation, it was found that single crystal Bi1-xSbx films (0${\sim}30\;{\AA}A$ can be prepared on Si(111)-$7{\times}7$. The transport properties of such films were characterized by in situ monolithic micro four-point probes [6]. The temperature dependence of the resistivity for the x=0.1 samples was insulating when the film thickness was $240\;{\AA}A$. However, it became metallic as the thickness was reduced down to $30\;{\AA}A$, indicating surface-state dominant electrical conduction. Figure 1 shows the Fermi surface of $40\;{\AA}A$ thick Bi0.92Sb0.08 (a) and Bi0.84Sb0.16 (b) films mapped by angle-resolved photoemission spectroscopy. The basic features of the electronic structure of these surface states were shown to be the same as those found on bulk surfaces, meaning that topological metals can be prepared at the surface of an ultrathin film. The details will be given in the presentation.

• Journal of Korean Society of Forest Science
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• v.112 no.3
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• pp.382-392
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• 2023

Recent reports have indicated a rapid increase in the frequency of sediment disasters due to climate change and other changes in the geological environment. Given this alarming situation and the recent increase in the frequency of land creep in Korea, systematic and efficient recovery and management of land creep areas is essential. The purpose of this study is to identify disaster vulnerability by conducting a physical exploration of land creep in San 4-1, Jayeon-ri, Gaegun-myeon, Yangpyeong-gun, Gyeonggi-do, and examine stability by identifying the overall geological structure of the affected ground. In addition, drilling surveys are conducted to verify the reliability of the measured data. The results of the study reveal that low specific resistance abnormalities are distributed in the upper part of the soil layer and weathering zone and that this section is a 50-120 m exploration line. It is also confirmed to be a low-hardness ground area where tensile cracks are observed. Therefore, there is a need for research focused on developing measures to reduce economic and social damage within the domestic context by continuously monitoring indicators of land creep and identifying land creep risks.

• Proceedings of the KOSOMBE Conference
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• v.1992 no.05
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• pp.27-47
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• 1992

Engineers have developed new instruments that aid in diagnosis and therapy Ultrasonic imaging has provided a nondamaging method of imaging internal organs. A complex transducer emits ultrasonic waves at many angles and reconstructs a map of internal anatomy and also velocities of blood in vessels. Fast computed tomography permits reconstruction of the 3-dimensional anatomy and perfusion of the heart at 20-Hz rates. Positron emission tomography uses certain isotopes that produce positrons that react with electrons to simultaneously emit two gamma rays in opposite directions. It locates the region of origin by using a ring of discrete scintillation detectors, each in electronic coincidence with an opposing detector. In magnetic resonance imaging, the patient is placed in a very strong magnetic field. The precessing of the hydrogen atoms is perturbed by an interrogating field to yield two-dimensional images of soft tissue having exceptional clarity. As an alternative to radiology image processing, film archiving, and retrieval, picture archiving and communication systems (PACS) are being implemented. Images from computed radiography, magnetic resonance imaging (MRI), nuclear medicine, and ultrasound are digitized, transmitted, and stored in computers for retrieval at distributed work stations. In electrical impedance tomography, electrodes are placed around the thorax. 50-kHz current is injected between two electrodes and voltages are measured on all other electrodes. A computer processes the data to yield an image of the resistivity of a 2-dimensional slice of the thorax. During fetal monitoring, a corkscrew electrode is screwed into the fetal scalp to measure the fetal electrocardiogram. Correlations with uterine contractions yield information on the status of the fetus during delivery To measure cardiac output by thermodilution, cold saline is injected into the right atrium. A thermistor in the right pulmonary artery yields temperature measurements, from which we can calculate cardiac output. In impedance cardiography, we measure the changes in electrical impedance as the heart ejects blood into the arteries. Motion artifacts are large, so signal averaging is useful during monitoring. An intraarterial blood gas monitoring system permits monitoring in real time. Light is sent down optical fibers inserted into the radial artery, where it is absorbed by dyes, which reemit the light at a different wavelength. The emitted light travels up optical fibers where an external instrument determines O2, CO2, and pH. Therapeutic devices include the electrosurgical unit. A high-frequency electric arc is drawn between the knife and the tissue. The arc cuts and the heat coagulates, thus preventing blood loss. Hyperthermia has demonstrated antitumor effects in patients in whom all conventional modes of therapy have failed. Methods of raising tumor temperature include focused ultrasound, radio-frequency power through needles, or microwaves. When the heart stops pumping, we use the defibrillator to restore normal pumping. A brief, high-current pulse through the heart synchronizes all cardiac fibers to restore normal rhythm. When the cardiac rhythm is too slow, we implant the cardiac pacemaker. An electrode within the heart stimulates the cardiac muscle to contract at the normal rate. When the cardiac valves are narrowed or leak, we implant an artificial valve. Silicone rubber and Teflon are used for biocompatibility. Artificial hearts powered by pneumatic hoses have been implanted in humans. However, the quality of life gradually degrades, and death ensues. When kidney stones develop, lithotripsy is used. A spark creates a pressure wave, which is focused on the stone and fragments it. The pieces pass out normally. When kidneys fail, the blood is cleansed during hemodialysis. Urea passes through a porous membrane to a dialysate bath to lower its concentration in the blood. The blind are able to read by scanning the Optacon with their fingertips. A camera scans letters and converts them to an array of vibrating pins. The deaf are able to hear using a cochlear implant. A microphone detects sound and divides it into frequency bands. 22 electrodes within the cochlea stimulate the acoustic the acoustic nerve to provide sound patterns. For those who have lost muscle function in the limbs, researchers are implanting electrodes to stimulate the muscle. Sensors in the legs and arms feed back signals to a computer that coordinates the stimulators to provide limb motion. For those with high spinal cord injury, a puff and sip switch can control a computer and permit the disabled person operate the computer and communicate with the outside world.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2000.11a
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• pp.3-4
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• 2000

Many researchers are interested in the synthesis and characterization of carbon nitride and diamond-like carbon (DLq because they show excellent mechanical properties such as low friction and high wear resistance and excellent electrical properties such as controllable electical resistivity and good field electron emission. We have deposited amorphous carbon nitride (a-C:N) thin films and DLC thin films by shielded arc ion plating (SAIP) and evaluated the structural and tribological properties. The application of appropriate negative bias on substrates is effective to increase the film hardness and wear resistance. This paper reports on the deposition and tribological OLC films in relation to the substrate bias voltage (Vs). films are compared with those of the OLC films. A high purity sintered graphite target was mounted on a cathode as a carbon source. Nitrogen or argon was introduced into a deposition chamber through each mass flow controller. After the initiation of an arc plasma at 60 A and 1 Pa, the target surface was heated and evaporated by the plasma. Carbon atoms and clusters evaporated from the target were ionized partially and reacted with activated nitrogen species, and a carbon nitride film was deposited onto a Si (100) substrate when we used nitrogen as a reactant gas. The surface of the growing film also reacted with activated nitrogen species. Carbon macropartic1es (0.1 -100 maicro-m) evaporated from the target at the same time were not ionized and did not react fully with nitrogen species. These macroparticles interfered with the formation of the carbon nitride film. Therefore we set a shielding plate made of stainless steel between the target and the substrate to trap the macropartic1es. This shielding method is very effective to prepare smooth a-CN films. We, therefore, call this method "shielded arc ion plating (SAIP)". For the deposition of DLC films we used argon instead of nitrogen. Films of about 150 nm in thickness were deposited onto Si substrates. Their structures, chemical compositions and chemical bonding states were analyzed by using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and infrared spectroscopy. Hardness of the films was measured with a nanointender interfaced with an atomic force microscope (AFM). A Berkovich-type diamond tip whose radius was less than 100 nm was used for the measurement. A force-displacement curve of each film was measured at a peak load force of 250 maicro-N. Load, hold and unload times for each indentation were 2.5, 0 and 2.5 s, respectively. Hardness of each film was determined from five force-displacement curves. Wear resistance of the films was analyzed as follows. First, each film surface was scanned with the diamond tip at a constant load force of 20 maicro-N. The tip scanning was repeated 30 times in a 1 urn-square region with 512 lines at a scanning rate of 2 um/ s. After this tip-scanning, the film surface was observed in the AFM mode at a constant force of 5 maicro-N with the same Berkovich-type tip. The hardness of a-CN films was less dependent on Vs. The hardness of the film deposited at Vs=O V in a nitrogen plasma was about 10 GPa and almost similar to that of Si. It slightly increased to 12 - 15 GPa when a bias voltage of -100 - -500 V was applied to the substrate with showing its maximum at Vs=-300 V. The film deposited at Vs=O V was least wear resistant which was consistent with its lowest hardness. The biased films became more wear resistant. Particularly the film deposited at Vs=-300 V showed remarkable wear resistance. Its wear depth was too shallow to be measured with AFM. On the other hand, the DLC film, deposited at Vs=-l00 V in an argon plasma, whose hardness was 35 GPa was obviously worn under the same wear test conditions. The a-C:N films show higher wear resistance than DLC films and are useful for wear resistant coatings on various mechanical and electronic parts.nic parts.

• Korean Chemical Engineering Research
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• v.49 no.5
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• pp.582-587
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• 2011

Holdup characteristics of bubble, wake and continuous liquid phases were investigated in bubble columns with viscous liquid media. Effects of column diameter(0.051, 0.076, 0.102 and 0.152 m ID), gas velocity($U_G$=0.02~0.16 m/s) and liquid viscosity(${\mu}_L$=0.001~0.050 $Pa{\cdot}s$) of continuous liquid media on the holdups of bubble, wake and continuous liquid phases were discussed. The three phase such as bubble, wake and continuous liquid phases were classified successfully by adapting the dual electrical resistivity probe method. Compressed filtered air and water or aqueous solutions of CMC(Carboxy Methyl Cellulose) were used as a gas and a liquid phase, respectively. To detect the wake as well as bubble phases in the bubble column continuously, a data acquisition system(DT 2805 Lab Card) with personal computer was used. The analog signals obtained from the probe circuit were processed to produce the digital data, from which the wake phase was detected behind the multi-bubbles as well as single bubbles rising in the bubble columns. The holdup of bubble and wake phases decreased but that of continuous liquid media increased, with an increase in the column diameter or liquid viscosity. However, the holdup of bubble and wake phases increased but that of continuous media decreased with an increase in the gas velocity. The holdup ratio of wake to wake to bubble phase decreased with an increase in the column diameter or gas velocity, however, increased with an increase in the viscosity of con-tinuous liquid media. The holdups of bubble, wake and continuous liquid media could be correlated in terms of operating variables within this experimental conditions as: ${\varepsilon}_B=0.043D^{-0.18}U_G^{0.56}{\mu}_L^{-0.13}$, ${\varepsilon}_W=0.003D^{-0.85}U_G^{0.46}{\mu}_L^{-0.10}$, ${\varepsilon}_C=1.179D^{0.09}U_G^{-0.13}{\mu}_L^{0.04}$.

• Proceedings of the KSEEG Conference
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• 2001.05b
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• pp.42-63
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• 2001

The detail survey on the Songsanri tomb site including the Muryong royal tomb was carried out during the period from May 1 , 1996 to April 30, 1997. A quantitative analysis was tried to find changes of tomb itself since the excavation. Main subjects of the survey are to find out the cause of infiltration of rain water and groundwater into the tomb and the tomb site, monitoring of the movement of tomb structure and safety, removal method of the algae inside the tomb, and air controlling system to solve high humidity condition and dew inside the tomb. For these purposes, detail survery inside and outside the tombs using a electronic distance meter and small airplane, monitoring of temperature and humidity, geophysical exploration including electrical resistivity, geomagnetic, gravity and georadar methods, drilling, measurement of physical and chemical properties of drill core and measurement of groundwater permeability were conducted. We found that the center of the subsurface tomb and the center of soil mound on ground are different 4.5 meter and 5 meter for the 5th tomb and 7th tomb, respectively. The fact has caused unequal stress on the tomb structure. In the 7th tomb (the Muryong royal tomb), 435 bricks were broken out of 6025 bricks in 1972, but 1072 bricks are broken in 1996. The break rate has been increased about 250% for just 24 years. The break rate increased about 290% in the 6th tomb. The situation in 1996 is the result for just 24 years while the situation in 1972 was the result for about 1450 years. Status of breaking of bircks represents that a severe problem is undergoing. The eastern wall of the Muryong royal tomb is moving toward inside the tomb with the rate of 2.95 mm/myr in rainy season and 1.52 mm/myr in dry season. The frontal wall shows biggest movement in the 7th tomb having a rate of 2.05 mm/myr toward the passage way. The 6th tomb shows biggest movement among the three tombs having the rate of 7.44mm/myr and 3.61mm/myr toward east for the high break rate of bricks in the 6th tomb. Georadar section of the shallow soil layer represents several faults in the top soil layer of the 5th tomb and 7th tomb. Raninwater flew through faults tnto the tomb and nearby ground and high water content in nearby ground resulted in low resistance and high humidity inside tombs. High humidity inside tomb made a good condition for algae living with high temperature and moderate light source. The 6th tomb is most severe situation and the 7th tomb is the second in terms of algae living. Artificial change of the tomb environment since the excavation, infiltration of rain water and groundwater into the tombsite and bad drainage system had resulted in dangerous status for the tomb structure. Main cause for many problems including breaking of bricks, movement of tomb walls and algae living is infiltration of rainwater and groundwater into the tomb site. Therefore, protection of the tomb site from high water content should be carried out at first. Waterproofing method includes a cover system over the tomvsith using geotextile, clay layer and geomembrane and a deep trench which is 2 meter down to the base of the 5th tomb at the north of the tomv site. Decrease and balancing of soil weight above the tomb are also needed for the sfety of tomb structures. For the algae living inside tombs, we recommend to spray K101 which developed in this study on the surface of wall and then, exposure to ultraviolet light sources for 24 hours. Air controlling system should be changed to a constant temperature and humidity system for the 6th tomb and the 7th tomb. It seems to much better to place the system at frontal room and to ciculate cold air inside tombs to solve dew problem. Above mentioned preservation methods are suggested to give least changes to tomb site and to solve the most fundmental problems. Repairing should be planned in order and some special cares are needed for the safety of tombs in reparing work. Finally, a monitoring system measuring tilting of tomb walls, water content, groundwater level, temperature and humidity is required to monitor and to evaluate the repairing work.