• BMB Reports
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• v.33 no.3
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• pp.268-275
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• 2000

In contrast to the pyrimidine (6-4)pyrimidone photoproduct [(6-4) adduct], its Dewar valence isomer (Dewar product) is low mutagenic and produces a broad range of mutations with a 42 % replicating error frequency. In order to determine the origin of the mutagenic property of the Dewar product, we used experimental NMR restraints and molecular dynamics to determine the solution structure of a Dewar·lesion DNA decamer duplex, which contains a mismatched base pair between the 3'-T residue and an opposed G residue. The 3'-T of the Dewar lesion forms stable hydrogen bonds with the opposite G residue. The helical bending and unwinding angles of the DW/GA duplex, however, are much higher than those of the DW/AA duplex. The stable hydrogen bonding of the G 15 residue does not increase the thermal stability of the overall helix. It also does not restore the distorted backbone conformation of the DNA helix that is caused by the forming of a Dewar lesion. These structural features implicate that no thermal stability, or conformational benefits of G over A opposite the 3'-T of the Dewar lesion, facilitate the preferential incorporation of an A. This is in accordance with the A rule during translesion replication and leads to the low frequent $3'-T{\rightarrow}C$ mutation at this site.

• Progress in Superconductivity
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• v.11 no.2
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• pp.152-157
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• 2010

We have fabricated the low noise liquid helium(LHe) dewar with a different shape of thermal shield to apply the 64-channel SQUID(Superconducting Quantum Interference Device) gradiometer. The first shape of thermal shield was made of an aluminum plate with a wide width of 100 mm slit and the other shape was modified with a narrow width of 20 mm slit. The two types of dewars were estimated by comparing the thermal noise and the signal-to-noise ratio(SNR) of magnetocardiography(MCG) using the $1^{st}$ order SQUID gradiometer system cooled each dewar. The white noise was different as a point of the dewar. The noise was increased as close as the edge of dewar, and also increased at the thermal shield with the more wide width slit. The white noise of the dewar with thermal shield of 100 mm slit was 6.5 fT/$Hz^{1/2}$ at the center of dewar and 25 fT/$Hz^{1/2}$ at the edge, and the white noise of the other one was 3.5 - 7 fT/$Hz^{1/2}$. We measured the MCG using 64-channel SQUID gradiometer cooled at each LHe dewar and compared the SNR of MCG signal. The SNR was improved of 10 times at the LHe dewar with a modified thermal shield.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.153-160
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• 2010

A magnetocardiogram (MCG) is a recording of the biomagnetic signals generated by cardiac electrical activity. Biomagnetic instruments are based on superconducting quantum interference devices (SQUIDs). A liquid cryogenic Dewar flask was used to maintain the superconductors in a superconducting state at a very low temperature (4 K). In this study, the temperature distribution characteristics of the liquid helium in the Dewar flask was investigated. The Dewar flask used in this study has a 30 L liquid helium capacity with a hold time of 5 d. The Dewar flask has two thermal shields rated at 150 and 40 K. The temperatures measured at the end of the thermal shield and calculated from the computer model were compared. This study attempted to minimize the heat transfer rate of the cryogenic Dewar flask using an optimization method about the geometric variable to find the characteristics for the design geometric variables in terms of the stress distribution of the Dewar flask. For thermal and optimization analysis of the structure, the finite element method code ANSYS 10 was used. The computer model used for the cryogenic Dewar flask was useful to predict the temperature distribution for the area less affected by the thermal radiation.

• Progress in Superconductivity
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• v.13 no.1
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• pp.1-6
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• 2011

Measurement of magnetic signals generated from electric activity of myocardium provides useful information for the functional diagnosis of heart diseases. Key technical component of the magnetocardiography (MCG) technology is SQUID. To measure MCG signals with high signal-to-noise ratio, sensitive SQUID magnetic field sensors are needed. Present magnetic field sensors based on Nb SQUIDs have field sensitivity good enough to measure most of MCG signals. However, for accurate measurement of fine signal pattern or detection of local atrial fibrillation signals, we may need higher field sensitivity. In addition to field sensitivity, economic aspect of the SQUID system is also important. To simplify the SQUID readout electronics, the output voltage or flux-to-voltage transfer of SQUID should be large enough so that direct measurement of SQUID output can be done using room-temperature preamplifiers. Double relaxation oscillation SQUID (DROS), having about 10 times larger flux-to-voltage transfers than those of DC-SQUIDs, was shown to be a good choice to make the electronics compact. For effective cancellation of external noise inside a thin economic shielded room, first-order axial gradiometer with high balance, simple structure and long-baseline is needed. We developed a technology to make the axial gradiometer compact using direct bonding of superconductive wires between pickup coil and input coil. Conventional insert has mechanical support to hold the gradiometer array, and the dewar neck has equal diameter with the dewar bottom. Boiling of the liquid He can generate mechanical vibrations in the gradiometer array due to mechanical connection structure. Elimination of the mechanical support, and direct mounting of the gradiometer array into the dewar bottom can reduce the dewar neck diameter, resulting in the reduction of liquid He consumption.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1312-1316
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• 2004

The Stirling refrigerators have been widely used for the cooling of the infrared detector and HTS to the cryogenic temperature. The Stirling refrigerator with the rotary compressor are applicable to the cooling device for the compact mobile thermal imaging system, because the refrigerators have the compact structure and light weight. The typical performance factors of the Stirling refrigerator are the cool-down time, cooling capacity at the desired temperature and the input power. And the above performance factors are depends on the thermal insulation characteristics of the Dewar. In this study, the steady thermal load of the Dewar and the performance of the Stirling refrigerator were measured. The results show the dependency of the input power and the charging pressure on the performance of the refrigerator.

• 한국초전도학회:학술대회논문집
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• 2007.07a
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• pp.50-50
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• 2007

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.203.2-203.2
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• 2012

IGRINS는 R=40,000의 해상도를 가지고 130K의 저온과 진공 환경에서, 한 번에 H와 K밴드 영역을 동시에 관측할 수 있도록 설계 된 적외선 분광기이다. 이 분광기에는 망원경 초점을 슬릿에 전달하는 IO (Input relay Optics) 모듈과 슬릿을 이미징하는 SVC (Slit Viewing Camera) 모듈 등 2개의 광학모듈이 있다. 광학모듈은 상온 및 저온(130K) 등 온도 변화와 진공 및 비진공 등 환경의 변화를 겪게 되는데, 이 과정에서 변화하는 광학성능을 시뮬레이션과 실험결과로 추적하였다. 시뮬레이션은 ZEMAX 소프트웨어를 사용하였고, 간섭계는 Phasecam 5030을 사용하였으며, IGRINS test dewar 내에 모듈을 설치하여 1,000 class급 청정도 환경에서 WFE를 측정 하였다. Test dewar는 빛이 통과할 수 있는 2개의 윈도우가 있는데, 윈도우는 test dewar 내부와 외부의 진공 및 온도 등 환경 변화에 따라 물리적인 변화가 발생하여 최종 WFE값에 영향을 준다. 본 연구에서는 IGRINS 광학모듈이 진공 및 냉각 상태에서 WFE가 변화하는 양상을 살펴봄으로써, 환경 변화에 따른 광학적 효과를 정량적으로 살펴본 결과를 소개할 것이며, 이 결과는 IGRINS 전체 광학계의 조립 및 정렬 시 환경 변화의 효과를 미리 예측할 수 있도록 하는 자료로 활용될 것이다.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.137-140
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• 1995

This paper describes the test results of magnetic field distributions of superconducting MRI magnet in an insert dewar. To get a very high homogeneous magnetic field, various shim coils are installed besides the main magnet. The operating currents of each shim coils are obtained from the exact measurements of the magnetic field. In this paper, we report the test results of the magnetic field distribution measurements with various shim coils.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.310-311
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• 2002

We designed a large bore superconducting solenoid as a source of magnetic field inside liquid-nitrogen-jacketed liquid helium dewar. The diameter of the sample space in the dewar is about 10.0 cm. Considering the space for thermal insulation between liquid helium and the sample tube, the solenoid bobbin has been designed to be 12.0 cm and the most inner layer of the solenoid 13.0 cm. The desired uniformity of the field, which is ~ $\pm$0.1％ of the central field amplitude deviation within ~5.0$^2$$\times$3.6 ㎤ with the shortest dimension along the solenoidal axis, restricted the length of the solenoid to be at least 41.14 cm.

• Progress in Superconductivity and Cryogenics
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• v.5 no.1
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• pp.133-135
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• 2003

Cryogenic systems are requirement for the operation of HTS power cables. In general, HTS power cables require temperature below 77K, a temperature that can be achieved from the liquid nitrogen at latm or sub-cooled LN2 above latm. HTS power cable needs sufficient refrigeration to overcome its low temperature heat loading. This loading typically cones in two forms : (1) heat leaks from the surroundings and (2) internal heat generation. This paper explains the cooling test system of 10m HTS power cable. This system is composed of storage dewar, auto fill system, core cryostat and cold-box. Storage dewar is a LN2 storage tank and auto fill system is a LN2 supply device to the sub-cooler, Core cryostat is a LN2 flow line. Cold box is a control unit of temperature and flow rate. It is composed of control valve, flow meter, sub-cooler and circulation pump, etc..