• 천문학회지
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• 제15권2호
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• pp.71-77
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• 1982

According to the star formation rate and metal enrichment rate given by the disk-halo model of Lee and Ann (1981), the two different forms of time-dependent initial mass function (IMF) and the present day mass function (PDMF) of nearby stars have been examined. It was shown that the constraint for the initial rapid metal enrichment requires the time-dependence of IMF at the very early phase ($t{\lesssim}5{\times}10^8$ yrs) of the solar neighborhood. The computed PDMF's show that the PDMF is nearly independent of any specific functional form of IMF as long as the latter includes a Gaussian distribution of log m. This result is due to the very small fractional mass $({\times}5%)$ of stars formed at the very early period during which the IMF is time-dependent. The computed PDMF suggests the presence of more numerous low mass stars than shown in Miller and Scalo's (1979) PDMF, supporting the possibility of the existence of low-velocity M dwarfs. According to the number distribution of stars with respect to [Fe/H], the mean age of these low mass star must be very old so as to yield the mean metal abundance $\bar{[Fe/H]}{\approx}-0.15$ for the stars in the solar neighborhood.

• Journal of Electrical Engineering and Technology
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• 제11권3호
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• pp.707-714
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• 2016

We present a piezoelectric energy harvester with stopper-engaged dynamic magnifier which is capable of significantly increasing the operating bandwidth and the energy (power) harvested from a broad range of low frequency vibrations (<30 Hz). It uses a mass-loaded polymer beam (primary spring-mass system) that works as a dynamic magnifier for another mass-loaded piezoelectric beam (secondary spring-mass system) clamped on primary mass, constituting a two-degree-of-freedom (2-DOF) system. Use of polymer (polycarbonate) as the primary beam allows the harvester not only to respond to low frequency vibrations but also generates high impulsive force while the primary mass engages the base stopper. Upon excitation, the dynamic magnifier causes mechanical impact on the base stopper and transfers a secondary shock (in the form of impulsive force) to the energy harvesting element resulting in an increased strain in it and triggers nonlinear frequency up-conversion mechanism. Therefore, it generates almost four times larger average power and exhibits over 250% wider half-power bandwidth than those of its conventional 2-DOF counterpart (without stopper). Experimental results indicate that the proposed device is highly applicable to vibration energy harvesting in automobiles.

• Nuclear Engineering and Technology
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• 제55권2호
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• pp.780-791
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• 2023

To study oscillation characteristic of steam and non-condensable gas direct contact condensation through multi-hole sparger at low mass flux, a series of experiments of pure steam and mixture gas condensation have been carried out under the conditions of steam mass flux of 20-120kg/m²s, water temperature of 20-95 ℃ and mass fraction of non-condensable gas of 0-5%. The regime map of pure steam condensation through multi-hole sparger is divided into steam chugging, separated bubble, aggregated bubble and escaping aggregated bubble. The bubbles behavior of synchronization in the same hole columns and desynchronized excitation between different hole columns can be found. The coalescence effect of mixture bubbles increases with water temperature and non-condensable gas content increasing. Pressure oscillation intensity of pure steam condensation first increases and then decreases with water temperature increasing, and increases with steam mass flux increasing. Pressure oscillation intensity of mixture gas condensation decreases with water temperature and non-condensable gas content increasing, which is significantly weaker than that of pure steam condensation. The oscillation dominant frequency decreases with the rise of water temperature and non-condensable gas content. The correlations for oscillation intensity and dominant frequency respectively are developed in pure steam and mixture gas condensation at low mass flux.

• Journal of Yeungnam Medical Science
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• 제39권4호
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• pp.285-293
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• 2022

Background: This study was conducted to analyze the effects of low skeletal muscle mass index (SMI) and obesity on aging-related osteoarthritis (OA) in the Korean population. Methods: A total of 16,601 participants who underwent a dual-energy X-ray absorptiometry and 3,976 subjects with knee X-rays according to the modified Kellgren-Lawrence (KL) system were enrolled. Knees of ≥KL grade 2 were classified as radiologic OA. The severity of joint space narrowing (JSN) was classified by X-rays as normal, mild-to-moderate, and severe JSN in radiologic OA. The subjects were grouped as normal SMI (SMI of ≥-1 standard deviation [SD] of the mean), low SMI class I (SMI of ≥-2 SDs and <-1 SD), and low SMI class II (SMI of <-2 SDs). Obesity was defined as a body mass index (BMI) of ≥27.5 kg/m². Results: The modified KL grade and JSN severity were negatively correlated with the SMI and positively correlated with BMI and age. The SMI was negatively correlated with age. JSN severity was significantly associated with a low SMI class compared to a normal SMI, which was more prominent in low SMI class II than class I. Obesity was significantly associated with more severe JSN, only for obesity with a low SMI class. Furthermore, patients with a low SMI class, regardless of obesity, were prone to having more severe JSN. Conclusion: This study suggested that a low SMI class was associated with aging and that an age-related low SMI was more critically related to the severity of JSN in OA.

• Mass Spectrometry Letters
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• 제8권2호
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• pp.44-47
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• 2017

Isothiazolinone derivatives are widely used in consumer products as disinfectants or preservatives, but there are growing concerns about their impact on human health. Therefore, rapid screening of these biocides is very important for proper control and regulation of potentially hazardous substances. To this end, low-temperature plasma (LTP) ionization mass spectrometry (MS) was investigated to demonstrate its potential for direct and selective analysis of isothiazolinones from sprayed aerosol samples. Benzisothiazolinone (BIT) was clearly identified from a commercial fabric deodorant using LTP ionization MS and MS/MS. LTP allowed selective ionization of BIT directly from the simply sprayed aerosol sample and illustrated its potential for fast screening without sample pre-treatments. Selective nature of LTP ionization, on the other hands, implicates use of LTP ionization MS as a general screening method for specific groups of hazardous chemicals in commercial products.

• Tribology and Lubricants
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• 제29권2호
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• pp.98-104
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• 2013

Cu-matrix-sintered brake pads and heat-resistant low-alloy steel are commonly applied to basic brake systems in high-energy moving machines. We analyzed how the tribological characteristics are influenced by the inertial mass. A high inertial mass decreased the friction coefficient by about 15% compared to a low inertial mass under all velocity conditions. The wear rates of the friction materials increased with the inertial mass. Thus, the inertial mass influences the friction coefficient and wear rate of the friction materials and disk but not the friction stability.

• Journal of Mechanical Science and Technology
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• 제16권2호
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• pp.255-261
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• 2002

A newly designed mass-detecting capillary viscometer uses a novel concept to continuously measure non-Newtonian fluids viscosity over a range of shear rates. A single measurement of liquid-mass variation with time replaces the now rate and pressure drop measurements that are usually required by capillary tube viscometers. Using a load cell and a capillary, we measured change in the mass flow rate through a capillary tube with respect to the time, m(t), from which viscosity and shear rate were mathematically calculated. For aqueous polymer solutions, excellent agreement was found between the results from the mass-detecting capillary viscometer and those from a commercially available rotating viscometer. This new method overcomes the drawbacks of conventional capillary viscometers meassuring non-Newtonian fluid viscosity. First, the mass-detecting capillary viscometer can accurately and consistently measure non -Newtonian viscosity over a wide range of shear rate extending as low as 1 s$\^$-1/. Second, this design provides simplicity (i. e., ease of operation, no moving parts), and low cost.

• 대한기계학회논문집B
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• 제27권2호
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• pp.163-172
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• 2003

Boiling heat transfer coefficients and pressure drops for R-22 and R-407C were measured in horizontal micro-channels. The test section is stainless steel tube, inner tube diameters are 1.8mm and 2.8mm, and the respective lengths are 1500mm and 3000mm. The range of mass flux is 300-600kg/$m^2$s and heat flux is 5-15kW/$m^2$. In this results, pressure drop increased linearly for both R-22 and R-407C with increased mass flux, but the increase of heat flux did not affect the pressure. In addition, the pressure drop was fairly increased in the high quality region rather than low quality region. In the range of low quality, the mass flux had a small affect on the heat transfer coefficients, however, in high quality region, the heat transfer coefficients increased even more with increasing mass flux. Under the low quality region and low mass flux, the heat transfer coefficients increased with increasing heat flux densities. The effects of inner tube diameter were clearly observed. Namely, the measured pressure drop inside inner tube diameter 1.8 mm is higher than 2.8 mm with increasing the mass flux and heat flux. Also, the measured local heat transfer coefficient inside inner tube diameter 1.8 mm is higher than 2.8 mm in the range of high qualities. The experimental data for R-407C compared with proposed correlation using pure refrigerant. The experimental data for R-407C was more decreased than the proposed correlation for pure refrigerant up to 50% or more.

• 세라미스트
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• 제21권3호
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• pp.249-269
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• 2018

In conventional MALDI-TOF mass spectrometry, analyte molecules are known to be ionized by mixing with organic matrix molecules. As the organic matrix molecules are made into small fragments, they generate unreproducible mass peaks such that MALDI-TOF mass spectrometry is nearly impossible in the low mass-to-charge (m/z) range (< 1000). Additionally, the dried sample mixed with matrix were made as inhomogeneous crystal on metal plate. When the laser radiation was made on the sample crystal, the amount of generated sample ion was observed to be quite different according to the radiation point. Therefore, the quantitative analysis was very difficult even for the sample spots at the same concentration for the conventional MALDI-TOF mass spectrometry. In this work, we present laser desorption/ionization (LDI) mass spectrometry based on solid-matrices for the quantitative analysis of small molecules in the low m/z range by using MALDI-TOF mass spectrometry: (1) Carbon based nanostructures; (2) Semiconductor based nanomaterials; (3) Metal based nanostructures.

• 스마트미디어저널
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• 제4권3호
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• pp.62-67
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• 2015

The trend keywords in ICT sector will be Big Data, Internet of Things, and Cloud Computing. The rear end to support those techniques requires a large-capacity storage technology of low-cost. Therefore, we proposed the prototype of low-cost and mass distributed storage system based on PC using open-source Ceph FS for SMB.