• Mass Spectrometry Letters
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• v.7 no.1
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• pp.21-25
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• 2016

Dual-channel nano-electrospray has recently become an ionization technique of great promise especially in biological mass spectrometry. This unique approach takes advantage of the mixing processes that occurs during electrospray. Understanding in more detail the fundamental principles influencing spray formation further study of the origins of the mixing processes: (1) in a Taylor cone region, (2) in charged droplets or (3) in both environments. The dual-channel emitters were made from borosilicate theta-shape glass tubes (O.D. 1.2 mm) and had a tip diameters of less than 4 μm. Electrical contact was achived by deposition of a thin film of an appropriate metal onto the surface of the emitter. The experimental investigation of the Taylor cone formation in a dual-channel electrospray emitter has been carried out by injection of polystyrene beads (diameter 3 μm) at very low concentrations into one of the channels of the non-tapered theta-glass tubes. High-speed camera experiments were set up to visualize the mixing processes in Taylor cone regions for dual-channel emitters. Mass spectra from dual nano-electrospray are presented.

• Journal of ILASS-Korea
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• v.29 no.2
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• pp.83-90
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• 2024

Understanding the fundamental characteristics of supersonic hydrogen jets is important for the optimization of combustion in hydrogen engines. Previous studies have used helium as a surrogate gas to characterize the hydrogen jet characteristics due to potential explosion risks of hydrogen. It was based on the similarity of hydrogen and helium jet structures in supersonic conditions that has been confirmed using hole-type injectors and large-cone-angle pintle-type injectors. However, the validity of using helium as a surrogate gas has not been examined for recent small-cone-angle pintle-type injectors applied to direct-injection hydrogen engines, which form a supersonic hollow cone near the nozzle and experience the jet collapse downstream. Differences in the physical properties of hydrogen and helium could alter the jet development characteristics that need to be investigated and understood. This study compares supersonic jet structures of hydrogen and helium injected by a small-cone-angle (50°) pintle-type hydrogen injector and discusses their differences and related mechanisms. Jet penetration length and dispersion angle are measured using the Schlieren imaging method under engine-like injection conditions. As a result, the penetration length of hydrogen and helium jets showed a slight difference of less than 5%, and the dispersion angle showed a maximum of 10% difference according to the injection condition.

• Fire Science and Engineering
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• v.33 no.4
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• pp.35-40
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• 2019

In this study, the mass flow rate of the heat release rate equation, which is the major factor of the oxygen consumption method, was analyzed for the fundamental investigation of the cone-calorimeter (5 m length and 0.3 m diameter). The shapes of a completely empty inside, 3 mm pore diameter mesh and pore diameter 10 mm honeycomb with 0.76 porosity were constructed using the cone-calorimeter. To calculate the mass flow rate, four bi-directional probes and thermocouples were installed in a uniform position in the vertical direction of flow. The velocity gradient and flow perturbation were measured from the increase in Reynolds number. As the flow capacity increased, the speed gradient increased in all three shapes relative to the turbulence intensity. In addition, the deviation of extended uncertainty to the mass flow was completely low in the order of empty space, mesh (d_p = 3 mm) and honeycomb (d_p = 10 mm and 𝜖 = 0.76) at the 95% confidence level. The results can be used in designs to improve the flow stability of the cone calorimeter.

• Journal of ILASS-Korea
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• v.16 no.1
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• pp.27-36
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• 2011

The impact force on the single and overlap region of twin spray was experimentally evaluated using visualization method in full cone type swirl nozzle spray. Visualization of spray was conducted to obtain the spray angle and breakup process. The photography/imaging technique, based on Particle Image Velocimetry (PIV) using high-speed camera, was adopted for the direct observation of droplet motion and axial velocity measurement, respectively. Droplet size was measured by Particle Motion Analyze System (PMAS). The purpose of this study is to provide fundamental information of spray characteristics, such as impact force, for higher etching factor in the practical wet etching system. It was found that the spray angle, axial velocity and impact force were increased with increasing the nozzle pressure while droplet size decreased with increasing the nozzle pressure. Droplet size increased as the distance from nozzle tip was decreased. The impact force of twin spray in the overlap region was about 63.29, 67.02, 52.41% higher than that of single spray at 40, 50 and 60 mm of nozzle pitch, respectively. Also, the nozzle pitch was one of the important factors in the twin spray characteristics.

• Journal of Biosystems Engineering
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• v.19 no.1
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• pp.17-21
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• 1994

This reasearch was performed to provide the fundamental intonation for the mechanization of Korean pine cone harvest when the shoot shearing method is adopted. Shear force and stress of pine cone shoots were measured and analyzed for this purpose. Samples are selected along their harvesting time and tested in 17 levels of shoot diameter from 10 to 26mm with 1mm increment. 1) Shear force-deformation characteristics showed that shoot reached its rupture point after 2 to 4 of bio-yield points. It was supposed that these multiple bio-yield points were caused by the discrete compression of wood parts which are composed of water, nutrient, resin, etc. 2) Required shear force to shear shoot was proportional to the square of shoot diamter, however, shear force for shoots of early harvesting time(Aug. 31) was proportional to the shoot diameter. Variance of shear force was increased as the harvesting time was delayed. Shear forces were distributed from 468N(Aug. 31, 12mm dia) to 4153N(Aug. 31, 26mm dia) disregarding the sampling date. 3) The average shear stresses by sampling dates were 744,822, and 883N/m2, respectively, and for the earlier shoot samples shear stress was quite smaller than the others. Shear stress was proportional to shoot diameter squared, and the effect of shoot diameter on the shear stress was decreased as harvesting time was delayed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.7
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• pp.26-31
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• 2003

In this paper, supersonic jets impinging on axisymmetric cone were investigated to obtain fundamental design data for jet deflector case of example being VTOL/STOL or rocket launch. It was of interest to study flow phenomena such as shock interactions and separation induced by shear layer. Experiments were conducted to obtain schlieren flow visualization and measurement of surface pressure. Numerical results are compared with the experimental result. The dominant feature of the flow is the shock pattern induced by the interaction between the cone shock and the barrel shock. This pattern can take a wide variety of forms depending on the structure of the free jet and strongly influences the form of the surface pressure distributions.

• ETRI Journal
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• v.27 no.4
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• pp.418-426
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• 2005

A calibration technique for a redundant inertial measurement unit (IMU) containing low-grade inertial sensors is proposed. In order to calibrate a redundant IMU that can detect and isolate faulty sensors, the fundamental coordinate frames in the IMU are defined and the IMU error is modeled based on the frames. Equations to estimate the error coefficients of the redundant IMU are formulated, and a test sequence using a 2-axis turntable is also presented. Finally, a redundant IMU with cone configuration is implemented using low-grade inertial sensors, and the performance of the proposed technique is verified experimentally.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.133-141
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• 2008

In this study, a new method for estimating the undrained shear strength $s_u$ of saturated clays using piezocone penetration test (CPTu) result is proposed. This is to develop more effective CPTu-based $s_u$ estimation method at lower cost with less uncertainty. For this purpose, a marine clay deposit is selected and tested through extensive experimental testing program including both in-situ and fundamental laboratory tests. The proposed method is based on a correlation between the undrained shear strength $s_u$ and the cone resistance $q_t$, without introduction of the total overburden stress into the $s_u-q_t$ correlation. As a result, no additional testing procedure for collecting undisturbed soils samples is required, which can reduce overall testing cost. To verify the proposed method, 4 test sites, which consist of a variety of soil conditions, are selected and used for comparison between measured and predicted undrained shear strength. From comparison, it is seen that predicted values of $s_u$ using the proposed method match well those from measured results.

• Bulletin of the Korean Mathematical Society
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• v.56 no.1
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• pp.111-130
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• 2019

The concepts of pseudocodeword and pseudoweight play a fundamental role in the finite-length analysis of LDPC codes. The pseudoredundancy of a binary linear code is defined as the minimum number of rows in a parity-check matrix such that the corresponding minimum pseudoweight equals its minimum Hamming distance. By using the value assignment of Chen and Kløve we present new results on the pseudocodeword redundancy of binary linear codes. In particular, we give several upper bounds on the pseudoredundancies of certain codes with repeated and added coordinates and of certain shortened subcodes. We also investigate several kinds of k-dimensional binary codes and compute their exact pseudocodeword redundancy.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.10
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• pp.53-59
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• 2004

A calibration technique for a redundant IMU with low-grade inertial sensors is proposed. In order to calibrate the redundant IMU that can detect and isolate a faulty sensor, the fundamental coordinate frames in the IMU are defined and the IMU error is modeled based on the frames. Equations to estimate the error coefficients of the redundant IMU are formulated, and a test sequence using the 2-axis rate table is also presented. Finally, a redundant IMU with cone configuration is implemented using the low-grade inertial sensors and the performance of the proposed technique is verified by some experiments.