• The Korean Journal of Ecology
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• v.26 no.6
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• pp.313-319
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• 2003

Dry weight loss and nutrient release from leaf litter for six tree species were studied using litter bag methods. The litter bags were incubated for f6 months on the forest floor in temperate deciduous forest in Mt. Cheonma, located at the middle part of Korean Peninsula. The changes in nutrient content and the rate of dry weight loss in leaf litter varied with litter types. The litter of Pinus densiflora showed the lowest rate of mass loss (k=0.33), nitrogen concentration (0.89%) and ash concentration (2.50%), while showed the highest C/N ratio (63.40). On the other hand, the litter of Acer pseudo-sieboldianum showed the fastest rate of mass loss (k=0.82), the highest nitrogen concentration (1.11%), and the lowest C/N ratio (49.40). During the decomposition, nitrogen, phosphorus and calcium in the leaf litters showed relatively slow decreasing pattern compared to other elements (carbon, potassium, magnesium, manganese and sodium), but potassium and sodium decreased at early stage of the decomposition for all leaf litters. Differences in annual decomposition rates of litter among species were consistent with the particular chemical characteristics of their leaf litters. The initial concentration of nitrogen was positively correlated with litter decomposition rate for six species, while litter decomposition rate of six species was negatively correlated with C:N ratio of initial leaf litters.

• Advances in Energy Research
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• v.8 no.1
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• pp.21-39
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• 2022

In this study, the first law of thermodynamics was used to establish a one-dimensional (1-D) thermal model for parabolic trough receiver (PTR) taking into account the pressure drop and kinetic energy loss effects of the heat transfer fluid (HTF) flowing inside the absorber tube. The validation of the thermal model with data from the SEGS-LS2 solar collector-test showed a good agreement, which is consistent with the previously established models for the conventional straight and smooth (CSS) receiver where the effects of pressure drop and kinetic energy loss were neglected. Based on the developed model and code, a comparative study of the newly designed parabolic trough S-curved receiver versus the CSS receiver was conducted and solar unit's performances were analyzed. Without any supplementary devices, the S-curved receiver enhances the performance of the parabolic trough module, with a maximum of 0.16% compared to CSS receiver with the same sizes and mass flow rates. Thermal losses were reduced by 7% due to the decrease in the temperature of the outer surface of the receiver tube. In addition, it has been shown that from a mass flow rate of 9.5 kg/s the heat losses of the S-curved receiver remain unchanged despite the improvement in the heat transfer rate.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.283-287
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• 2015

Within the context of the hugely successful SAGE-LMC and SAGE-SMC surveys, Spitzer photometry observations of the Large and Small Magellanic Clouds have revealed millions of infrared point sources in each galaxy. The brightest infrared sources are generally dust producing and mass-losing evolved stars, and several tens of thousands of such stars have been classified. After photometrically classifying these objects, the dust production by several kinds of evolved stars - such as Asymptotic Giant Branch stars and Red Supergiants - can be determined. SAGE-Spec is the spectroscopic follow-up to the SAGE-LMC survey, and it has obtained Spitzer-IRS $5-40{\mu}m$ spectroscopy of about 200 sources in the LMC. Combined with archival data from other programs, observations at a total of ~1000 pointings have been obtained in the LMC, while ~250 IRS pointings were observed in the SMC. Of these, a few hundred pointings represent dust producing and mass-losing evolved stars, covering a range in colors, luminosities, and thus mass-loss rates. Red Supergiants and O-rich and C-rich AGB stars - the main dust producers - are well represented in the spectroscopic sample. This paper will summarize what we know about the mineralogy of dust producing evolved stars, and discuss their relative importance in the total dust budget.

• Journal of The Korean Astronomical Society
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• v.47 no.6
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• pp.219-233
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• 2014

The main site of dust formation is believed to be the cool envelopes around AGB stars. Nearly all AGB stars can be identified as long-period variables (LPVs) with large amplitude pulsation. Shock waves produce by the strong pulsation and radiation pressure on newly formed dust grains drive dusty stellar winds with high mass-loss rates. IR observations of AGB stars identify various dust species in different physical conditions. Radio observations of gas phase materials are helpful to understand the overall properties of the stellar winds. In this paper, we review (i) classification of AGB stars; (ii) IR two-color diagrams of AGB stars; (iii) pulsation of AGB stars; (iv) dust around AGB stars including dusty stellar winds; (v) dust envelopes around AGB stars; (vi) mass-loss and evolution of AGB stars; and (vii) contribution of AGB dust to galactic environments. We discuss various observational evidences and their theoretical interpretations.

• The KSFM Journal of Fluid Machinery
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• v.2 no.1 s.2
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• pp.64-72
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• 1999

CSCM upwind flux difference splitting compressible Navier-Stokes method has been used to predict the transonic flows in a centrifugal compressor diffuser. The modified cyclic. TDMA and the mass flux boundary conditions were used as boundary conditions of the diffuser analysis. Broad flow separation on the suction surface near the hub and shroud was observed from the results of the mass flow rates 5.8, 6.0 and 6.2kg/s at 27000 rpm. The three-dimensional flow analysis predicted successfully that the static pressure increased and the total pressure decreased through the flow passage of the channel diffuser when compared to two-dimensional analysis due to the strong effect of the three-dimensional flow. The mass averaged loss coefficients and pressure coefficients were also studied.

• Korean Journal of Agricultural and Forest Meteorology
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• v.5 no.2
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• pp.87-93
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• 2003

Litterfall and litter decomposition represent a major contribution to the carbon and nutrient inputs in a forest ecosystem. We measured litterfall quantity and nutrient dynamics in decomposing litter for two years at the Kwangneung broadleaf natural forest (DK site) in Korea. Litterfall was collected in circular littertraps (collecting area : 0.25 $m^2$) and mass loss rates and nutrient release patterns in decomposing litter were estimated using the litterbag technique employing 30 cm ${\times}$ 30 cm nylon bags with 1.5 mm mesh size. Total annual litterfall was 5,627 kg/ha/yr and leaf litter accounted for 61 % of the litterfall. The leaf litter quantity was highest in Quercus serrata, fallowed by Carpinus laxiflora and C. cordata, etc., which are dominant tree species in the site. Mass loss from decomposing leaf litter was more rapid in C. laxiflora and C. cordata than in Q. serrata litter. About 77% of C. laxiflora and 84% of C. cordata litter disappeared, while about 48% in Q. serrata litter lost over two years. Lower mass loss rates of Q. serrata litter may be attributed to the difference of substrate quality such as lower nutrient concentrations compared with the other litter types. Nutrient concentrations (N, P, Mg) of three litter types except for potassium (K) increased compared with initial nutrient concentrations of litter over the study period. Compared with Q. serrata litter, nutrients (N, P, K, Ca, Mg) in C. laxiflora and C. cordata litter were released rapidly. The results suggest that litter mass loss and nutrient dynamic processes among tree species vary considerably in the same site conditions.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.1
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• pp.1-8
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• 1999

In the present paper an attempt has been made to simulate the secondary injection-primary flow interaction in the conical rocket nozzle and to derive the performance of secondary injection thrust vector control(SITVC) system. Complex three-dimensional flowfield induced by the secondary injection is numerically analyzed by solving unsteady three-dimensional Euler equation with Beam and Warming's implicit approximate factorization method. Emphasized in the present study is the effect of secondary injection such as secondary mass flow rates and the momentum of secondary/primary nozzle flow mass rates upon the gross system performance parameters such as thrust ratio, specific impulse ratio and deflection angle. The results obtained in terms of system performance parameters show that lower secondary mass flow rate is advantageous for to reduce secondary specific impulse loss. It is further found that the nozzle with secondary jet injected downstream and interacting with fast primary flow is preferable for efficient and stable SITVC over the wide range of use with the penalty of side specific impulse loss.

• Safety and Health at Work
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• v.6 no.1
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• pp.1-8
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• 2015

Time-loss injuries are still a major occurrence in Canada, injuring thousands of Canadian workers each year. With obesity rates on the rise across the country, as well as around the world, it is important that the possible effects of obesity in the workplace be fully understood, especially those effects linked to lost-time injuries. The aim of this paper was to evaluate predictors of workplace lost-time injuries and how they may be related to obesity or high body mass index by examining factors associated with lost-time injuries in the health care sector, a well-studied industry with the highest number of reported time loss injuries in Canada. A literature review focusing on lost-time injuries in Registered Nurses (RNs) was conducted using the keywords and terms: lost time injury, workers' compensation, occupational injury, workplace injury, injury, injuries, work, workplace, occupational, nurse, registered nurse, RN, health care, predictors, risk factors, risk, risks, cause, causes, obese, obesity, and body mass index. Data on predictors or factors associated with lost-time injuries in RNs were gathered and organized using Loisel's Work Disability Prevention Management Model and extrapolated upon using existing literature surrounding obesity in the Canadian workplace.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.85.1-85.1
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• 2014

The progenitors of Type Ibc supernovae (SNe Ibc) have been believed to be massive Wolf-Rayet (WR) stars, formed either through stellar wind mass loss or Roche-lobe outflow in a binary system. But observations indicate that ordinary SNe Ibc have relatively low ejecta masses (~2 Msun), which is not compatible with the WR star scenario for SN Ibc progenitors. On the other hand, helium stars in binary systems which can be produced via mass transfer are also suggested as a possible candidate for SN Ibc progenitors. Binary star evolution models predict that SN Ibc progenitors having final masses of 3-7 Msun can be produced, but their observational properties are not well understood. In this study, we present the parameter study on the observational constraints of helium stars of 3-5 Msun in binary systems using evolutionary models and the atmospheric radiative transfer code CMFGEN. We present the predicted magnitudes and spectra of helium stars in optical bands for different wind velocity profiles and mass loss rates. We also present those observables of the progenitor binary system considering O-type companion stars. Based on the results, we discuss the expected observational properties of SN Ibc progenitors in binary systems. In particular, we discuss the constraints on the progenitor of the SN Ib iPTF13bvn of which progenitor candidate has been identified for the first time in pre-explosion images among SNe Ibc.

• Journal of the Korean Dietetic Association
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• v.19 no.2
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• pp.103-111
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• 2013

In this study, we examined chewing frequency, eating rates, and food consumption volume according to the body mass index of male and female college students. Twenty-five male college students were divided into a normal weight male group (<23 body mass index, n=14) and an obese male group (${\geq}23$ body mass index, n=11). Twenty-five female college students were divided into a normal weight female group (<23 body mass index, n=21) and an obese female group (${\geq}23$ body mass index, n=4). Subjects were provided with abundant fried rice and allowed to consume it at their own pace. Chewing frequency, total mealtime, rate of eating, consumption volume, calorie intake, and the amount of one bite were measured. There were no significant differences in chewing frequency, total mealtime, rate of eating, consumption volume, calorie intake, and the amount of one bite between the normal and obese male groups. There were also no significant differences in chewing frequency, consumption volume, calorie intake, and the amount of one bite between the normal and obese female groups. However, the obese female group had a significantly shorter mealtime and significantly higher eating rate compared with the normal group. Thus, our study suggests that females who eat a meal for a longer time may reduce their food intake, consequently inducing body weight loss.