• Journal of ILASS-Korea
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• v.11 no.2
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• pp.105-112
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• 2006

A unique feature of fluidic atomizers is that the nozzle geometry produces a thin capillary Jet which is forced to oscillate on a 2-dimensional plane through the use of a passive feedback mechanism. The objective of the current work is to characterize the influence of the stagnation pressure at the nozzle exit, jet oscillation and stretching on the breakup properties of the capillary ligament. To achieve this, shadow graph technique is used to measure size, shape, velocity and the number density of the droplets as a function of the position within the spray fan. The breakup length, defined as the radial distance from the breakup point, is analyzed as a function of the non-dimensional parameters. Finally, a kinematic model is developed to simulate the breakup of the oscillating jets at low stagnation pressures. Using the existing jet breakup theories, the model is used to predict the size and diameter distribution of the droplets after primary atomization.

• Journal of the Korean Institute of Telematics and Electronics
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• v.23 no.2
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• pp.264-268
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• 1986

A thchnique has been studied for the measurement of the spectral loss and the cut-off wave length, at which the first high-order mode disappears. The near-field patterns of a fiber which is excited by a variable wavelength source are used for the measurement of cut-off wavelength. Because of the absorptive phenomenon of OH- molecular vibration, spectral loss of a single mode optical fiber sample is 5.6dB/km at 1380 nm wavelength and 1dB/km at 1240 nm wavelength. From the near field intensity patterns and the mode field diameter graph for the half power width, the cut-off wavelength of the fiber is measured to be 1120 nm.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.15 no.4
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• pp.1-8
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• 2007

Spray characteristics of a unlike triplet injector were investigated experimentally. Spray images and SMD of droplet were measured to evaluate the spray characteristics injected by liquid/gas combinations. G-L-G(Gas-Liquid-Gas), L-G-L(Liquid-Gas-Liquid) type of injector were used by changing the gas and liquid feed lines. The SMD graph shows that the droplet sizes decrease in the out of radial direction at a fixed gas Reynolds number. The SMD value of decreasing tendency shows that the more ethyl alcohol ratio increase, the more SMD value decrease.

• Korean Journal of Materials Research
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• v.29 no.7
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• pp.443-450
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• 2019

Thermal management is a critical issue for the development of high-performance electronic devices. In this paper, thermal conductivity values of mild steel and stainless steel(STS) are measured by light flash analysis(LFA) and dynamic thermal interface material(DynTIM) Tester. The shapes of samples for thermal property measurement are disc type with a diameter of 12.6 mm. For samples with different thickness, the thermal diffusivity and thermal conductivity are measured by LFA. For identical samples, the thermal resistance($R_{th}$) and thermal conductivity are measured using a DynTIM Tester. The thermal conductivity of samples with different thicknesses, measured by LFA, show similar values in a range of 5 %. However, the thermal conductivity of samples measured by DynTIM Tester show widely scattered values according to the application of thermal grease. When we use the thermal grease to remove air gaps, the thermal conductivity of samples measured by DynTIM Tester is larger than that measured by LFA. But, when we did not use thermal grease, the thermal conductivity of samples measured by DynTIM Tester is smaller than that measured by LFA. For the DynTIM Tester results, we also find that the slope of the graph of thermal resistance vs. thickness is affected by the usage of thermal grease. From this, we are able to conclude that the wide scattering of thermal conductivity for samples measured with the DynTIM Tester is caused by the change of slope in the graph of thermal resistance-thickness.

• The Journal of the Korean dental association
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• v.12 no.9
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• pp.691-694
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• 1974

The trends of restoration on abrased teethis mostly based on gnathology or on practical experience. This study was performed on plaster models from 60 young men whose teeth and occlusion are clinically normal. A pair, upper and lower models, were mounted on HANAU articulator. Iron ball bearing 0.2mm 0.5mm 0.7mm and 1.0mm in diameter was attached on mesiobuccal cusp of upper first molar. [table I] Long ribbon shape of cold cure resin was inserted and jaw was closed gently so as not to move disturb original position of iron ball. The resin bite registration was measured minimun thickness from each lingual cusps of upper jaw and buccal cusps of lower jaw by means of Bowley gauge. The results were as follows (graph). 1) The distance from upper lingual cusps and lower buccal cusps: backward cusps showed smaller than standard cusp (upper mesio-buccal cusp) and forward cusps showed longer than standard. 2) The measurements from upper lingual cusps are not coincide with lower buccal cusps.

• Korean Journal of Agricultural Science
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• v.6 no.2
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• pp.192-197
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• 1979

Spread factors were tried to determine the diameter of airborne droplet emitted: from the sprayer by the measurements of airborne droplet diameter emitted from the uniform size droplet producer and impression diameter on Kromekote card or Eucalypt's leaf in the different dilute concentration with Geigy Red Herbicide Dye from 0.5% to 2% by weight. The results abtained were as follows; The general form of the equation in the relationship between airborne droplet and impression diameter on Kromekote card or Eucalypt's leaf was an exponential equation as follows; $$Y=aX^b$$ which gave a linear relation on log-log graph paper. The spread factor seemed to be larger in the thin dilute concentration than in the thick dilute concentration. The spread factor was remarkably smaller on Eucalypt's leaf than on Kromekote card due to the penetration of liquid into the leaf and the stomata of the epidermis. The calculated equation of the mean depth of the droplet sprayed on Eucalypt's leaf was the same form as $Y=aX^b$, which implied that the spray liquid was distributed in surplus in accordance with the diameter of the droplet larger than the optimum size droplet to control insect and disease.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.6
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• pp.788-794
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• 1985

A study on the number density in a dual beam LDV is carried out with moving particles of various irregular arrangements. Ratious of the particle diameter to the particle to the fringe Spacing are D/.delta. = 0.3, 0.5, 1.0 and 1.5. In the case of the small number of moving particles(N<10), the visibility is influenced much by the difference of the phase of particles for one side fringe and the change in visibility is shown remarkable. In the case of the larger number of particles, the decreasing rate for visibility on the graph is smooth because the effect of the phase difference of particles is decreased by more unitorm distribution of particles over fringes. And the formula of the number density on the basis of probability is fairly compared with experimental values.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.2
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• pp.78-86
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• 2019

Aluminum, which is a metal fuel contained in the composite solid propellant, is not ignited and burned on the combustion surface by the oxide film, and it partially melts and coalesces with surrounding aluminum particles. For the evaluation and design of the propellant performance, modeling was performed to predict the size and distribution of agglomerated particles, and the size and distribution of agglomerates were compared and verified through experiment. The predicted values showed the tendency to decrease with pressure as in the experiment, but the error increased as the pressure increased. The agglomerated particle distribution graph showed a difference in the volume fraction although the diameter at the peak was the same.

• Fibers and Polymers
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• v.7 no.4
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• pp.404-413
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• 2006

This study examines multiple quality optimization of the injection molding for Polyether Ether Ketone (PEEK). It also looks into the dimensional deviation and strength of screws that are reduced and improved for the molding quality, respectively. This study applies the Taguchi method to cut down on the number of experiments and combines grey relational analysis to determine the optimal processing parameters for multiple quality characteristics. The quality characteristics of this experiment are the screws' outer diameter, tensile strength and twisting strength. First, one should determine the processing parameters that may affect the injection molding with the $L_{18}(2^1{\times}3^7)$ orthogonal, including mold temperature, pre-plasticity amount, injection pressure, injection speed, screw speed, packing pressure, packing time and cooling time. Then, the grey relational analysis, whose response table and response graph indicate the optimum processing parameters for multiple quality characteristics, is applied to resolve this drawback. The Taguchi method only takes a single quality characteristic into consideration. Finally, a processing parameter prediction system is established by using the back-propagation neural network. The percentage errors all fall within 2%, between the predicted values and the target values. This reveals that the prediction system established in this study produces excellent results.

• Imaging Science in Dentistry
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• v.30 no.3
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• pp.155-158
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• 2000

The purpose of this paper is to explain the making procedure and the usage of receiver operating characteristic (ROC) curve for interpretation of radiographic images. The conventional radiograms obtained after the creation of the lesions in the acrylic plates and were enhanced in color. The observer were informed of which tooth to examine, the 'a priori' probability of a lesion present and the approximate diameter of the lesions. The two groups of films were interpreted separately by the same observer using the same rating scale. The following rating scale was used: A; definitely no lesion, B; probably no lesion, C; not sure, D; probably a lesion, and E; definitely a lesion. In analysis, for each observer the diagnostic results in terms of true positive (TP) and false positive (FP) decisions were plotted on a graph. The lowest point on the graph represents the TP and FP when only decisions designated as E according to the rating scale are included. The next point shows the TP and FP values when diagnoses designated as D are added and so forth. By connecting such plot points, a receiver operating characteristic (ROC) curves is obtained. The area under the curve represents the diagnostic accuracy resulting from a diagnostic performance at pure chance level and a value of 1.0 at perfect performance. This method has been known as an useful method to detect the minute difference for each radiographic technic, each observer and for the different lesion depths.