• Journal of the Korean Society of Safety
• /
• v.21 no.5 s.77
• /
• pp.17-21
• /
• 2006

In this study, SPCC cross-tension type specimens produced under various spot welding conditions were tensile and fatigue tested. Decrease of 2 kA in normal current condition of 10 kA caused a large amount of reduction in both static joining strength and fatigue life. And 2 kA increase resulted in increase of static joining strength and an increase in low cycle regime but a decrease in high cycle regime, revealing the fact that fatigue strength rather than static joining strength would be a major factor during design process in view of the body endurance. As a results of estimating the fatigue lifetimes of various types of spot weld specimens. equivalent stress intensity factor is the proper parameter for predicting the lifetimes of various types of specimens. which can be expressed as ${\Delta}K_{eq}(N/nm^{1.5})=11550N^{-0.36}_{f}$.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.3 s.234
• /
• pp.376-383
• /
• 2005

In the paper we investigate characteristics of a transitional behavior from a premixed flame to a triple flame in a lifted flame according to the change of equivalence ratio. In previous study, we showed that the stabilized laminar lifted flame regime is categorized by regimes of premixed flame, triple flame and critical flame. A gas-chromatograph is used to measure concentration field, a smoke-wire system is used to measure streak line, and a PIV system is used to measure velocity field in lifted flame. In the visualization experiment of smoke wire, the flow divergence and redirection reappeared in premixed flame as well as triple flame. Thus we cannot express the flame front of lifted flame has a behavior of triple flame with only flow divergence and redirection. In PIV measurement, flow velocity for those three flames has minimum value at the tip of flame front. To differentiate triple flame and premixed flame, $\Phi$ value of partially premixed fraction is employed. The partially premixed fraction $\Phi$ was constant in premixed flame. In critical flame small gradient appears over the whole regime. In triple flame, typical diffusion flame shape is obtained as parabolic distribution type due to diffusion flame trailing.

• Tribology and Lubricants
• /
• v.32 no.6
• /
• pp.195-200
• /
• 2016

This study examines the wear behavior of mild steel pins mated against alloyed tool steel discs in a pin-on-disc type sliding test machine and provides specific clarification regarding the effects of disc hardness on the wear behavior of a mating mild steel pin. The analysis confirms these effects through the observation of differences in the wear rates of the mild steel pins at low sliding speed ranges. These differences occur even though the hardness of the mating disc does not affect the wear characteristic curve patterns for the sliding speeds, regardless of the wear regime. In the running-in wear regime, increasing the hardness of the mating disc results in a decrease in the wear rates of the mild steel pins at low sliding speed ranges. However, in the steady-state wear region, the wear rate of a pin mated against the 42DISC is greater than the wear rate of a pin mated against the 30DISC, which has a lower hardness value. This means that the tribochemical reactivity of the mating disc, which is based on hardness value, influences the wear behavior of mild steel at low sliding speed ranges. In particular, oxides with higher oxygen contents, such as $Fe_2O_3$ oxides, form predominantly on the worn surface of the 42DISC. On the contrary, the wear behavior of mild steel pins at high sliding speed ranges is nearly unaffected by the hardness of the mating disc.

• Advances in nano research
• /
• v.12 no.5
• /
• pp.489-499
• /
• 2022

Nanofluids have recently triggered a substantial scientific interest as cooling media. However, their stability is challenging for successful engagement in industrial applications. Different factors, including temperature, nanoparticles and base fluids characteristics, pH, ultrasonic power and frequency, agitation time, and surfactant type and concentration, determine the nanofluid stability regime. Indeed, it is often too complicated and even impossible to accurately find the conditions resulting in a stabilized nanofluid. Furthermore, there are no empirical, semi-empirical, and even intelligent scenarios for anticipating the stability of nanofluids. Therefore, this study introduces a straightforward and reliable intelligent classifier for discriminating among the stability regimes of alumina-water nanofluids based on the Zeta potential margins. In this regard, various intelligent classifiers (i.e., deep learning and multilayer perceptron neural network, decision tree, GoogleNet, and multi-output least squares support vector regression) have been designed, and their classification accuracy was compared. This comparison approved that the multilayer perceptron neural network (MLPNN) with the SoftMax activation function trained by the Bayesian regularization algorithm is the best classifier for the considered task. This intelligent classifier accurately detects the stability regimes of more than 90% of 345 different nanofluid samples. The overall classification accuracy and misclassification percent of 90.1% and 9.9% have been achieved by this model. This research is the first try toward anticipting the stability of water-alumin nanofluids from some easily measured independent variables.

• Journal of the Korean Ceramic Society
• /
• v.55 no.5
• /
• pp.510-514
• /
• 2018

Colloidal semiconductor quantum dots (QDs), because of the novel optical and electrical properties that stem from their three-dimensional confinement, have attracted great interest for their potential applications in such fields as bio-imaging, display, and opto-electronics. However, many semiconductors that can be exploited for QD applications contain toxic elements. Herein, we synthesized non-toxic ZnTe/ZnSe (core/shell) type-II QDs by pyrolysis method. Because of the unique type-II character of these QDs, their emission can range over an extended wavelength regime, showing photoluminescence (PL) from 450 nm to 580 nm. By optimizing the ZnSe shell growth condition, resulting ZnTe/ZnSe type-II QDs shows PL quantum yield up to ~ 25% with 35 nm PL bandwidth. Using a simple two step cation exchange reaction, we also fabricated ZnTe/ZnSe type-II QDs with absorption extended over the whole visible region. The visible-light sensitized heavy metal free ZnTe/ZnSe type-II QDs can be relevant for opto-electronic applications such as displays, light emitting diodes, and bio-imaging probes.

• 한국사회정책
• /
• v.25 no.1
• /
• pp.345-375
• /
• 2018

This study examines labour market and unemployment protection policies as a configuration in 12 OECD countries in order to investigate how countries from different regime conform to or diverse from previous welfare state regime discussion, and to examine its relationship with poverty and inequality. In analyzing the combination of the unemployment insurance, the unemployment assistance, and active labour market policy, firstly, fuzzy scores of unemployment insurance was calculated by analyzing the strictness of eligibility, duration of benefit and the generosity of income replacement rate. For unemployment assistance, the ratio of public assistance expenditure to the GDP in each country and the ratio of unemployment benefit level to the average wage in each country have been considered. As for the active labour market policy, the total expenditure per GDP of this policy was converted into fuzzy points and analyzed. As a result, 5 types in 2005 and 6 types in 2010 were generated. Specifically, 'assistance type(iAp)', 'insurance type (Iap)', 'comprehensive safety net type (IAP)', 'weak safety net type(iap)' were analyzed. This paper suggested policy implication for South Korean case, which consistently had high score for weak safety net type(iap).

• Proceedings of the Korea Society for Energy Engineering kosee Conference
• /
• 1995.05a
• /
• pp.185-198
• /
• 1995

This is an experimental study conducted to visualize the nucleate boiling phenomena and flow regimes occurring inside the liquid pool in a closed two-phase thermosyphon. To meet this purpose, an annular-type thermosyphon was designed and manufactured using a glass tube and a stainless steel tube, being assembled axisymmetrically. The heat to be supplied to the working fluid is generated within a very thin layer of stainless steel tube wall by applying a high frequency electromagnetic field through the induction coil, axisymmetrically set around the evaporator zone. Some important results were as follows ; 1) Considering the structural complexity of the tested thermosyphon, it showed good performance for the range of heat flux 2＜ q" ＜25kW/$m^2$ and saturation vapor pressure, 0.1＜Pv＜1.1bar 2) different type of nucleating boiling regimes were observed as described below, -Pulse boiling regime : Flow pattern changed cyclically with time during 1 cycle of pulse boiling process. The onset of Nucleation was followed by expulsive growing of vapor bubble, resulting in the so called blow-up phenomenon, massive expulsion of large amount of liquid around the bubble. -Transient : Some spherical vapor bobbles were observed growing out from 2~3 nucleating sites, that was dispersed at the lower part of the heated tube wall in the liquid pool. But the rest upper region above the nucleating sites were filled with churns or bubbles of vapor. -Continuous nucleate boiling regime : The whole zone of evaporator was filled with lots of spherical vapor bubbles, and the bubbles showed tendency to decrease in diameter as the heat flux increased.ased.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.2 no.3
• /
• pp.56-61
• /
• 2003

This paper described about on-machine profile measurement of aspheric surfaces using contact probing technique in ultra precision machine. A contact probe has been designed as a sensing device to obtain measuring resolutions in nanometer regime using a circle leaf spring mechanism and a capacitive-type sensor. The contact probe which is installed on the z-axis is In touch with the aspheric objects which is fixed on the spindle of the diamond turning machine(DTM) during the measuring procedure. The x, z-axis motions of the machine are monitored by a set of two orthogonal plane mirror type laser interferometers. As a results, the developed contact probe on-machine measurement system showed 10 nanometers repeatability with a ${\pm}2{\sigma}$ and uncertainty of 200 nmPv.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.06a
• /
• pp.90-93
• /
• 2003

This paper described about the ultra-precision profile measurement of aspheric surfaces using contact probing technique. A contact probe has been designed as a sensing device to obtain measuring resolutions in nanometer regime utilizing a circle leaf spring mechanism and a capacitive-type sensor. The, contact probe is attached on the z-axis during measurement while aspheric object are supported on the diamond turning machine(DTM). The machine xz-axis motions are monitored by a set of two orthogonal plane mirror type laser interferometers. Experimental results show that the contact probing technique developed of on-machine measurement system in this investigation is capable of providing a repeatability of 10 nanometers with a $\pm$20 uncertainty of 200nmPv.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2000.05a
• /
• pp.603-606
• /
• 2000

This dissertation is concerned with ultra-precision profile measurement of aspheric surfaces using contact probing technique. A contact probe has been designed as a sensing device to obtain measuring resolutions in nanometer regime utilizing a leaf spring mechanism and a capacitive-type sensor. The contact probe is attached on the z-axis during measurement while aspheric objects are supported on an precision xy-stage whose lateral motions are monitored by a set of two orthogonal plane mirror type laser interferometers. Experimental results show that the contact probing technique developed in this investigation is capable of providing a repeatability of 50 nanometers with a $\pm$3$\sigma$ uncertainty of 300 nanometers. Thermal disturbance is found the most significant factor that should be precisely controlled for accurate measurement.