• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.163-166
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• 2003

This paper presents the results of a series of performance tests for the Stilting cryocooler. Infrared sensor systems incorporating cryocoolers are required to be qualified to the appropriate environmental specification. Linear drive Stilting cryocooler have matured to the stage of undergoing formal qualification test program The thermal environmental test of the Stilting cryocooler is presented in this paper. We performed that low and high temperature keeping test from －4$0^{\circ}C$ to ＋6$0^{\circ}C$ and operating test at high and low temperature cyclic range with acceptance tests performed at scheduled intervals. Cooling capacity was determined as a function of cooler components temperatures at the compressor, hot end and cold tip. Tests performed on this cooler have been successful with a measured cooling performance of more than 0.8W＠80K for 23$^{\circ}C$ ambient temperature with 40 $W_{ac}$ input power.

• Progress in Superconductivity and Cryogenics
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• v.14 no.1
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• pp.34-37
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• 2012

In this paper, configurations and performance of a pulse tube engine (PTE) are investigated. The configuration of PTE is basically designed by using a concept of energy flow. The configurations of PTE are classified as a PTE with two pistons and a PTE with one piston. First, the PTE with two pistons is simulated and the Carnot efficiency is about 41 %. The phase difference of between motion of two pistons located at expander and compressor mainly effects the performance of the PTE. Second, the PTE with one piston is designed. From a concept of analogy, the piston of compressor is replaced by a compliance tube and a resonator. The PTE with one piston is identical with a thermoacousic engine and has the large volume because the compliance tube and resonator are consisted of large volume tubes. Therefore, we will consider each usefulness of the compact PTE with two pistons and the huge PTE with one piston for PTE applications and the judgement of feasibility.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.320-323
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• 2003

This paper presents the results of a series of performance tests for the Stilting cryocooler. A free piston and free displacer(FPFD) Stilting cryocooler for cooling infrared and cryo-sensors is currently under development at KIMM. Our coolers are specifically designed to work in the thermal imaging device and to meet requirements such as cooling capacity, COP and high reliability. In this work, Stilting cryocooler is designed, manufactured and fabricated, and performance characteristics for the cooling capacity / applied input power and cool down time are investigated. This cooler delivers approximately 0.9W cooling at 80K for 30W ~ 40W of input power. And, It takes approximately 2 minutes to cool down to 80K at the ambient temperature of 23$^{\circ}C$.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.167-170
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• 2003

This paper presents the results of a series of performance tests for the Stilting cryocooler. A free piston and free displacer(FPFD) Stilting cryocooler for cooling infrared and cryo-sensors is currently under development at KIMM. Our coolers are specifically designed to work in the thermal imaging device and to meet requirements such as cooling capacity, COP and high reliability. In this work, Stilting cryocooler is designed, manufactured and fabricated, and performance characteristics for the vibration, acoustic noise, EMI and leak rate are evaluated. Vibration outputs are measured to 20KHz for compressor and expander, respectively. And, the objective of noise test is a noise level, less than 30㏈ at 5 m. EMI tests are carried out according to the standard MIL-STD-461C tests RE01 and RE02. Leak test for the Stilting cryocooler is performed by bombing method.

• Progress in Superconductivity and Cryogenics
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• v.7 no.3
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• pp.43-46
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• 2005

A Protomodel Space Infrared Cryogenic System (PSICS) cooled by a stirling cryocooler was designed. The PSICS has an IR sensor inside a cold box which is cooled by a stilting cryocooler with refrigeration capacity of 500mw at 80K in a vacuum vessel. It is important to minimize heat load for reducing background thermal noise. In order to design the cryogenic system of low heat load and to reduce heat load, we did several numerical analyses and tested using boil-off calorimetry with liquid nitrogen to measure the heat leak of the system. In this paper, we present the results obtained by thermal analysis and heat load measurement for designing the PSICS.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.4B no.3
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• pp.108-113
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• 2004

This paper presents methods to improve performance of the power supply system in a NASA deep space explorer. In the Stirling engine driven reciprocating Brushless DC (BLDC) generator, the accurate position information of the prime mover is important to diagnose the performance of the engine and prevent distortion of the output power. Since sensors to detect the position are fragile and unreliable, and conventional sensorless techniques have drawbacks in the low speed region, a novel sensorless position detection technique for the prime mover has been proposed and verified. Another major issue of the generator for the spacecraft is power density maximization. The mass of the power system is important to the mass of the satellite. Therefore, the components of the spacecraft should be lightweight. Conventional rectification methods cannot achieve the maximum power possible due to non-optimal current waveforms. The optimal current waveform for maximizing power density and minimizing machine size and weight in a nonsinusoidal power supply system has been derived, incorporated in a control system, and verified by simulation work.

• Communications of the Korean Mathematical Society
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• v.16 no.2
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• pp.319-332
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• 2001

The main object of this paper is first to give tow contiguous analogues of a well-known hypergeometric summation formula for $_2$F$_1$(1/2). We then apply each of these analogues with a view to evaluating the sums of several classes of series in terms of Psi(or Digamma) and the Zeta functions. Relevant connections of the series identities presented here with those given elsewhere are also pointed out.

• Journal of applied mathematics & informatics
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• v.39 no.1_2
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• pp.45-56
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• 2021

D.S. Kim et al. [9] considered some identities and relations for Korobov type numbers and polynomials. In this work, we investigate the degenerate Korobov type Changhee polynomials and the (p,q)-poly-Korobov polynomials. We give a generalization of the Korobov type Changhee polynomials and the (p,q) poly-Korobov polynomials. We prove some properties and identities and explicit relations for these polynomials.

• Progress in Superconductivity and Cryogenics
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• v.8 no.3
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• pp.63-69
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• 2006

This paper describes the effect of rotating frequency on the pulse tube of Stirling type pulse tube refrigerator. Various conditions were analyzed by two-dimensional analysis with several dominant non-dimensional parameters. With the additional pressure term influenced by centrifugal force in rotating condition, the linearized conservation equations of mass, momentum, energy of the gas were solved to obtain the first order variables and calculate the enthalpy flow in rectangular coordinates. The rotational effect in pulse tube for the refrigerator's performance were quantitatively evaluated. According to the first order analysis, the enthalpy flow decreases with the rotating speed.

• Journal of the Korean Society for information Management
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• v.33 no.1
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• pp.7-32
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• 2016

This study has measured interdisciplinarity using a topic modeling, which automatically extracts sub-topics based on term information appeared in documents group unlike the traditional top-down approach employing the references and classification system as a basis. We used titles and abstracts of the articles published in top 20 journals for the past five years by the 5-year impact factor under the category of 'Information & Library Science' in JCR 2013. We applied 'Discipline Diversity' and 'Network Coherence' as factors in measuring interdisciplinarity; 'Shannon Entropy Index' and 'Stirling Diversity Index' were used as indices to gauge diversity of fields while topic network's average path length was employed as an index representing network cohesion. After classifying the types of interdisciplinarity with the diversity and cohesion indices produced, we compared the topic networks of journals that represent each type. As a result, we found that the text-based diversity index showed different ranking when compared to the reference-based diversity index. This signifies that those two indices can be utilized complimentarily. It was also confirmed that the characteristics and interconnectedness of the sub-topics dealt with in each journal can be intuitively understood through the topic networks classified by considering both the diversity and cohesion. In conclusion, the topic modeling-based measurement of interdisciplinarity that this study proposed was confirmed to be applicable serving multiple roles in showing the interdisciplinarity of the journals.