• Journal of IKEEE
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• v.15 no.4
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• pp.305-312
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• 2011

A primary interest of this work is to develop an efficient and powerful repetitive pulser system for the application of ultra wide band generation. The important component of the pulser system is a small-sized coaxial type spark gap with planar electrodes filled with SF6 gas. A repetitive switching action by the coaxial spark gap generates two consecutive pulses in less than a microsecond with rise times of a few hundred picoseconds (ps). A set of several parameters for the repetitive switching of the spark gap is required to be optimized in charging and discharging systems of the pulser. The parameters in the charging system include a circuit scheme, circuit elements, the applied voltage and current ratings from power supplies. The parameters in the discharging system include the spark gap geometry, electrode gap distance, gas type, gas pressure and the load. The characteristics of the spark gap discharge, such as breakdown voltage, output current pulse and recovery rate are too dynamic to control by switching continuously at a high pulse repetition rate (PRR). This leads to a low charging efficiency of the spark gap system. The breakthrough of the low charging efficiency is achieved by a parallel operation of two spark gaps system. The operational behavior of the two spark gaps system is presented in this paper. The work has focused on improvement of the charging efficiency by scaling the PRR of each spark gap in the two spark gaps system.

• Advances in aircraft and spacecraft science
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• v.3 no.3
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• pp.243-257
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• 2016

The increase of air traffic volume has brought an increasing amount of issues related to carbon and NOx emissions and noise pollution. Aircraft manufacturers are concentrating their efforts to develop technologies to increase aircraft efficiency and consequently to reduce pollutant discharge and noise emission. Ultra High By-Pass Ratio engine concepts provide reduction of fuel consumption and noise emission thanks to a decrease of the jet velocity exhausting from the engine nozzles. In order to keep same thrust, mass flow and therefore section of fan/nacelle diameter should be increased to compensate velocity reduction. Such feature will lead to close-coupled architectures for engine installation under the wing. A strong jet-wing interaction resulting in a change of turbulent mixing in the aeroacoustic field as well as noise enhancement due to reflection phenomena are therefore expected. On the other hand, pressure fluctuations on the wing as well as on the fuselage represent the forcing loads, which stress panels causing vibrations. Some of these vibrations are re-emitted in the aeroacoustic field as vibration noise, some of them are transmitted in the cockpit as interior noise. In the present work, the interaction between a jet and wing or fuselage is reproduced by a flat surface tangential to an incompressible jet at different radial distances from the nozzle axis. The change in the aerodynamic field due to the presence of the rigid plate was studied by hot wire anemometric measurements, which provided a characterization of mean and fluctuating velocity fields in the jet plume. Pressure fluctuations acting on the flat plate were studied by cavity-mounted microphones which provided point-wise measurements in stream-wise and spanwise directions. Statistical description of velocity and wall pressure fields are determined in terms of Fourier-domain quantities. Scaling laws for pressure auto-spectra and coherence functions are also presented.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.59 no.1
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• pp.35-43
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• 2023

Sensory evaluation of shucking pressure, pressure holding time, seeding method, difference in full shucking rate in the aquaculture area and shucking oyster was performed using an ultra-high pressure oyster shucking machine. The reaching time for each target pressure is 2.2-2.4 MPa/sec in the range of 180 MPa to 240 MPa. had a rate of pressure rise. There was a difference of 0.5-1.7℃ in the range of 24-27℃ in the seawater temperature before and after the pressure treatment inside the pressure vessel, but there was no specific increase or decrease in seawater temperature. When only the shucking pressure is increased without the pressure holding time, the critical shucking pressure at which the oyster shell is opened and the flesh is peeled in the range of 200 to 220 MPa. When the critical shucking pressure is reached, the oyster sample in the closed vessel is expected to be shucked by about 40%. If there is no pressure holding time when judged only by full shucking, an increase in pressure of about 1.5 MPa is required to further shuck 3% of the oyster population. The oyster samples cultivated in the south coast of Korea were subject to full shucking under the conditions of 220 MPa shucking pressure and two minutes (120 seconds) of pressure holding time, and the difference in the pressure of the oysters according to the oyster seeding method and the farming area was minute. Finally, the condition of 220 MPa of shucking pressure and three minutes of pressure holding time was the best at 1.52 when the result of the sensory evaluation performed manually was set to 1.0. Next was 1.4 under the conditions of 220 MPa of shucking pressure and one minute of pressure holding time (60 seconds), and 1.3 under the condition of 220 MPa and two minutes of pressure holding time (120 seconds). Therefore, it is considered that the most desirable shucking conditions, considering the efficiency and sensory evaluation results, are the conditions of 220 MPa shucking pressure and two to three minutes of pressure holding time.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.224-227
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• 1999

A high power deep-water sonar transducer of FFR (Free Flooded Ring) type has been designed using a coupled FE-BEM. The present sonar transducer is composed of rectangular piezoelectric ceramics and pie-shaped steels (or the advantage of simple fabrication. The dynamics of the sonar transducer is modelled in three dimensions and is analyzed with external electrical excitation conditions. Different results are available such as steady-state frequency response for TX and RX displacement modes, directivity patterns, back-scattering patterns, bandwidths, transmitting voltage responses and receiving sensitivity responses. The TV response shows a very high acoustic pressure of 150 dB/lV (ref $1{\mu}Pa$ at 1m) at 1900 Hz. This ultra high power response of the sonar transducer indicates a new possibility of the sonar transducer development.

• Journal of Magnetics
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• v.8 no.3
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• pp.124-127
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• 2003

HDDR (hydrogenation, disproportionation, desorption, recombination) and mechanical milling processes have been applied to the $SmCo_{5}$ alloy in an attempt to produce a highly coercive powder. The $SmCo_{5}$ alloy had very high structural stability under the hydrogen atmosphere and the 1:5 phase was only partially disproportionated under up to 10 kgf/$\textrm{cm}^2$ hydrogen gas. The partially disproportionated material was recombined not into 1:5 phase after the HDDR, but rather into multi-phase mixture consisting of 1:5, 2:17, 2:7 and 1:7 phases. The $SmCo_{5}$ alloy HDDR-treated with hydrogen up to 10 kgf/$\textrm{cm}^2$ had poor coercivity. For a useful HDDR to prepare a high coercivity $SmCo_{5}$ alloy powder, much higher hydrogen pressure well exceeding 10 kgf/$\textrm{cm}^2$ would be required. The $SmCo_{5}$ alloy lump was amorphized by an intensive mechanical milling, and it was crystallised ultra-finely by a subsequent optimum annealing. The optimally annealed material had very high coercivity, and it was found that the mechanical milling followed by an annealing was an effective way of producing highly coercive $SmCo_{5}$ alloy powder.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.207-210
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• 2005

In order to investigate the influence of the homo buffer layer on the microstructure of the ZnO thin film, undoped ZnO buffer layer were deposited on sapphire (0001) substrates by ultra high vaccum pulsed laser deposition (UHV-PLD) and molecular beam eiptaxy (MBE). After high temperature annealing at $600^{\circ}C$ for 30min, undoped ZnO buffer layer was deposited with various oxygen pressure (35~350mtorr). On the grown layer of undoped ZnO, Arsenic-doped(l, 3wt%) ZnO layers were deposited by UHV-PLD. The optical property of the ZnO was analyzed by the photoluminescence (PL) measurement. From $\Theta-2\Theta$ XRD analysis, all the films showed strong (0002) diffraction peak, and this indicates that the grains grew uniformly with the c-axis perpendicular to the substrate surface. Field emission scanning electron microscope (FE-SEM) revealed that microstructures of the ZnO were varied with oxygen pressure, arsenic doping level, and the deposition method of undoped ZnO buffer layers. The films became denser and smoother in the cases of introducing MBE-buffer layer and lower oxygen pressure during As-doped ZnO deposition. Higher As-doping concentration enhanced the columnar-character of the films.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.3
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• pp.285-293
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• 2009

Thermal infrared cameras have been conducted actively in various application areas, such as military, medical service, industries and cars. Because of their characteristic of sensing the radiant heat emitted from subjects in the range of long-wavelength($3{\sim}5{\mu}m$ or $8{\sim}12{\mu}m$), and of materializing a vision system, when general optics materials are used, they don't react to the light in the range of long-wavelength, and can't display their optic functions. Therefore, the materials with the feature of higher refractive index, reacting to the range of long-wavelength, are to be used. The kinds of materials with the characteristic of higher refractive index are limited, and their features are close to those of metals. Because of these metallic features, the existing producing method of optical systems were direct manufacturing method using grinding method or CAD/CAM, which put limit on productivity and made it difficult to properly cope with the increasing demand of markets. GASIR, a material, which can be molded easily, was selected among infrared ray optics materials in this study, and the optical system was designed with two Aspheric lenses. Because the lenses are molded in the environment of high temperature and high pressure, they require a special metallic pattern. The metallic pattern was produced with materials with ultra hardness that can stand high temperature and high pressure. As for the lens mold, GMP(Glass Molding Press) of the linear transfer method was used in order to improve the productivity of optical systems for thermal infrared cameras, which was the goal of this paper.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.1
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• pp.13-20
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• 2010

Airborne particulate matters have two modes of size distributions of coarse mode and fine mode. The coarse mode which is formed by break down mechanism of large particles has a peak around the $100\;{\mu}m$, and the fine mode formed by condensation and build up mechanism of evaporated vapors has a peak at several ${\mu}m$. The coarse mode particles can be removed easily by conventional collecting equipments such as a cyclone, an electrostatic precipitator, and a filter, however the fine mode particles can not be collected easily. Usually the fine mode particles are generated in the high temperature conditions especially through boilers and incinerators, so the high efficient and temperature filter is essential for the filtration. In this study, a nano ceramic filter for the removal of fine particles in the high temperature is developed and tested for several characteristics. The nano ceramic filter has double layer of micro and nano structure and the pressure drop and the filtration efficiency for $0.31\;{\mu}m$ at 3 cm/s are 15.45 mmAq, and 96.75%, respectively. The thermal conductivity is $0.038\;W/m{\cdot}K$, and the coefficient of water vapor permeability is $3.63\;g/m^2{\cdot}h{\cdot}mmHg$. It is considered that the sensible heat exchange rate is very poor because the low thermal conductivity but it has high potential to exchange latent heat.

• Korean Journal of Food Science and Technology
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• v.32 no.2
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• pp.373-379
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• 2000

Low salt fermented anchovy was stored at $25^{\circ}C$ for a period of 20 days from the time of ultra-high pressure treatment under different operating conditions, such as magnitude of pressure($(200{\sim}500\;MPa)$, temperature$(20{\sim}50^{\circ}C)$ and treatment time$(5{\sim}20\;min)$ with viable cell count(VCC) and quality assessments conducted at regular intervals. VCC decreased logarithmically during storage. Lower values of VCC in the treated samples were observed compared to the untreated. A gradual increase in peroxide value was noticed during storage, compared to those of the untreated which showed a sudden rise. Thiobarbituric acid value decreased initially and remained at that level before rising almost exponentially between 12 and 20 days. Volatile basic nitrogen increased gradually during storage. Amino nitrogen remained almost constant up to 20 days, regardless of any conditions investigated. High pressure treatment maintained better quality during storage at $25^{\circ}C$ by reducing the viable cell count in low salt fermented anchovy.

• FOCUS: LIFE SCIENCE
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• no.1
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• pp.1.1-1.4
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• 2024

This article provides comprehensive guidance on the maintenance, cleaning, regeneration, and storage of silica-based HPLC (High-Performance Liquid Chromatography) columns. The general considerations emphasize the importance of using in-line filters and guard cartridges to protect columns from blockage and irreversible sample adsorption. While these measures help, contamination by strongly adsorbed sample components can still occur over time, leading to an increase in back pressure, loss of efficiency, and other issues. To maximize column lifetime, especially with UHPLC (Ultra-High Performance Liquid Chromatography) columns, it is advisable to use ultra-pure solvents, freshly prepared aqueous mobile phases, and to filter all samples, standards, and mobile phases. Additionally, an in-line filter system and sample clean-up on dirty samples are recommended. However, in cases of irreversible compound adsorption or column voiding, regeneration may not be possible. The document also provides specific recommendations for column cleaning procedures, including the flushing procedures for various types of columns such as reversed phase, unbonded silica, bonded normal phase, anion exchange, cation exchange, and size exclusion columns for proteins. The flushing procedures involve using specific solvents in a series to clean and regenerate the columns. It is emphasized that the flow rate during flushing should not exceed the specified limit for the particular column, and the last solvent used should be compatible with the mobile phase. Furthermore, the article outlines the storage conditions for silica based HPLC columns, highlighting the impact of storage conditions on the column's lifetime. It is recommended to flush all buffers, salts, and ion-pairing reagents from the column before storage. The storage solvent should ideally match the one used in the initial column test chromatogram provided by the manufacturer, and column end plugs should be fitted to prevent solvent evaporation and drying out of the packing bed.