• The Journal of Asian Finance, Economics and Business
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• v.7 no.3
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• pp.157-165
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• 2020

This paper estimates the optimum level of reserves in Vietnam based on the approach of reserves' cost-benefit and sovereign risk which is one of developing countries' characteristics. The cost of reserves is the opportunity cost when holding reserves. The benefit of reserves is the loss due to country's default in case that there is no reserves to finance external debt payment. The optimum reserves is found out by minimizing the total of opportunity cost and loss due to country's default with the probability of default. Through the usage of HP Filter method for calculating the loss due to country's default, ARDL regression for the risk premium model and lending rate of VND as proxy for opportunity cost together with the Vietnamese economic data in the period of 2005 - 2017, the empirical results show that the optimum reserves in Vietnam is almost higher than the actual reserves during the research period except the point of Q3/2008 and the last point of research period - Q4/2017. Therefore, Vietnam should continue to increase reserves for safety but Vietnam does not need pushing quickly the speed of increasing reserves. In addition, controlling Vietnamese optimum reserves is necessary to help the actual reserves become reasonable.

• Solar Energy
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• v.10 no.1
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• pp.14-21
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• 1990

The entropy generation rate in a fin-tube heat exchanger is investigated as a basis for thermodynamic optimization associated with single fin-tube heat exchanger. The entropy generation (irreversibility)analysis is used to find the optimum design factor and investigate total entropy generation, optimum dimensions of fin length, tube inner and outer diameters, and fin spacing on the variation of design factors. The results of this study are as follows: As the outer diameter increases, optimum !in spacing and fin length increase but the entropy generation and optimum inner diameter decrease; As fin thickness increases, the entropy generation of system and optimum fin spacing increase; As fin length increases, entropy generation and optimum outer diameter increase.

• KSBB Journal
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• v.13 no.5
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• pp.547-553
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• 1998

For the efficient production of a new exo-polysaccharide from Ganoderma lucidum ASI 7004, the optimum conditions and methods in submerged cultivation were investigated with an airlift fermenter system. The optimum aeration rate was 2.5 Wm at the initial pH 5.0 and 28$^{\circ}C$. The increase of dissolved oxygen concentration by pure oxygen supply during cultivation did not improved the exo-polysaccaride production and the mycelial growth. The maximum exo-polysaccharide production and the mycelial growth under the optimum culture condition were obtained in media of glucose 60g/L, yeast extract 6g/L, (NH4)2HPO4 1g/L and KH2PO4 0.5g/L. Under these optimum medium and culture conditions, about 7.15g/L of exo-polysaccharide and 13.9g/L of mycelial growth were producted, respectively.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.1 no.1
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• pp.109-116
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• 2002

Resently, reduction of industrial products in size and weight has increased by the application of micro-drill for gadgets of high precision and gave rise to a great interest in a micro-drilling. Due to the lack of tool stiffness and the chip packing, micro-drilling requires not only the robust tool structure which has not affected by the vibration, but also the effective drilling methods designed to prevent tool fracture from cutting troubles. Firstly, this paper presents a new manufacturing process of micro-drill for improving the product rate and an optimum shape of micro-drill for lengthening the tool life, and secondly suggests between tool life and drilling torque acquired in the inprocess monitoring system.

• Journal of Korean Society for Quality Management
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• v.33 no.4
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• pp.111-116
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• 2005

This paper considers the problem of optimally choosing the sub-process means of a mixture production process where two important ingredients are mixed. The quantity of each ingredient is controlled through each corresponding sub-process. The values of the sub-process mean directly affect the defective rate, production, scrap and reprocessing costs for the mixture production process. After inspecting every incoming item, each conforming item is sold in a regular market for a fixed price and any nonconforming item is scraped. A model is constructed on the basis of the selling price, production, inspection, and scrap and reprocessing costs. The goal is to determine the optimum sub-process mean values based on maximizing expected profit function relating selling price and cost components. A method of finding the optimum sub-process means is presented when the quantities of the two ingredients are assumed to be normally distributed with known variances. A numerical example is given and numerical studies are performed.

• Journal of Korean Institute of Industrial Engineers
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• v.8 no.1
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• pp.3-12
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• 1982

Three types of repair-ordering polices for the production facility with r-out-of-n configuration are considered. Policies are characterized by states of the system and two types of lead times ; regular lead time and expedited lead time. Optimum repair-ordering policy is determined by minimizing the cost rate for the system. Optimum policy consists of the type of policies and repair-ordering time. Variations of the optimum policies are observed with respect to variations of lead times and associated ordering costs and downtime cost, respectively.

• Journal of the Korean Institute of Landscape Architecture
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• v.26 no.2
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• pp.219-228
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• 1998

This study was investigated a optimum planting density of urban public park in seoul. Eight species commonly usd as landscape plants were selected. The survey was conducted to measure hight and width of the trees by five years interval. The results are summarized as follows. The average annual growth rates of the trees after planting were 7.4% in height 11.7% in width. Faster grown trees than average growth rate of the survey tres wee Metasequoia, glyptostroboides and Acer buergerianum, While the slower grown trees were Pinus koraiensis, Ginkgo biloba and Zelkova serrata. The average grown trees were Pinus strobus, Pinus densiflora and Acer palmatum . The planting density of survey area was 0.20tree/$m^2$. The optimum planting density was kept until five years after planting, however overcrowding density was found beyond five years after planting. This study also found the density of ten years after planting reaches about 3 times of optimum density.

• Microbiology and Biotechnology Letters
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• v.22 no.5
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• pp.557-560
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• 1994

The optimum medium composition for the production of L-tryptophan with Klebsiella pnuemoniae pheA tyrA trpE trpR/pSC 101-trp$^{+}$ and the effect of precusors in the optimum medium were studied. The specific growth rate in the optimum medium was almost the same as that in the basal medium, the former showing 1.01 and the latter 1.07 hr $$^{-1}$, but the produced tryptophan was increased 45% in the optimum medium. The maximum amount of produced tryptophan was 159 mg/l within 14 hours. Tryptophan production was ceased by casamino acid addition over 4 g/l in medium, but cell maSS increased with its addition. Indole and anthranilate as precusors had toxic effect on growth and tryptophan production at experimented concentration range (over 20 mg/l), but L-serine had good effect on tryptophan production, resulting in 175 mg/l tryptophan within 14 hours.

• Korean Journal of Microbiology
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• v.10 no.1
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• pp.1-8
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• 1972

This experiment was carried out to investigate the physiological characteristics of isolated bacteria, Ferrobacillus ferooxidans from copper mine water in Korea. The results obtained were as follows ; 1. The optimum pH range for the growth of these bacteria was 2.0-3.0 and optimum temperature was $20^{\circ}C$-$30^{\circ}C$. 2. The oxidation curves of ferrous iron to the ferric iron ran parallel with the growth curves. 3. The optimum nitrogen concentration was 400-800 ppm and the minimal flow rate of air for the maximal growth of the bactria was 70 ml air/min./200ml medium. 4. The growth of these bacteria was inhibited by the absence of ferrous iron and by the addition of sulfur. 5. Ferrous iron at a concentration of 9000 ppm, appeared to be optimum for the most rapid growth of Ferrobacillus ferrooxidans.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.454-457
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• 2005

Voloxidizer for hot cell demonstration that handle spend fuel of high radiation virulence in limited space should become a small size and not scatter in its exit. This study determine optimum velocity of $U_3O_8$ using Newton-Raphson Method. We have conducted fortran programing on the Newton-Raphson Method, obtained a theory results and, predicted optimum velocity on the particle size distribution of $U_3O_8$. We have conducted experimentation using acrylic experimental device for verification of theory method, sampled and analyzed using the particle size analyzer In the results, we have found maximum $5\~7\%$ error rate in the comparative value of theory and experimentation. Optimum velocity and experimental results of $U_3O_8$ for scatter prevention have applied for design of demonstration voloxidizer, and produced operation condition of voloxidizer.