• Progress in Superconductivity and Cryogenics
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• v.22 no.4
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• pp.62-66
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• 2020

We fabricated superconducting quantum interference devices (SQUIDs) based on Nb Josephson junctions, and characterized the key parameters of the SQUIDs. The SQUIDs are double relaxation oscillation SQUIDs (DROSs) having larger flux-to-voltage transfer coefficient than the standard DC-SQUIDs. SQUID sensors were fabricated by using Nb junction technology consisted of a DC magnetron sputtering and a conventional photolithography process. In multichannel SQUID systems for whole-head magnetoencephalography measurement with a helmet-type SQUID array, we need about 336 SQUID sensors for each system. In this paper, we fabricated a few hundred SQUID sensors, measured the critical current, flux modulation voltage and decided if each tested SQUID can be used for the multichannel systems. As the criterion for the acceptance of the sensors, we chose the critical current and amplitude of the modulation voltage to be 8 ㎂ and 80 ㎶, respectively. The average critical current of the SQUIDs was 10.58 ㎂. The typical flux noise of the SQUIDs with input coil shorted was 2 μΦ0/√Hz at white region.

• Bulletin of the Korean Chemical Society
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• v.24 no.4
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• pp.446-452
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• 2003

Some new nanohybrid materials have been synthesized by intercalating the oxotitanium(IV) meso-tetrakis(4- sulfonatophenyl) porphyrin$(O=Ti^{(IV)} TSPP)$ into the Zn/Al layered double hydroxides (LDHs), and their structures and photophysical properties have been investigated by various laser spectroscopic techniques. According to the XRD pattern of the synthesized nanohybrid materials, the macrocycle plane of $O=Ti^{(IV)}$ TSPP are grafted perpendicular to the LDH layers. The $O=Ti^{(IV)}$ TSPP-intercalated LDH exhibits band broadening of the absorption spectrum and a blue shift of Q-band as compared to that observed in solution. Resonance Raman spectral measurements demonstrate that the positively charged LDHs give rise to a slight decrease of the electronic density of the porphyrin ring accompanying a small change of the electronic distribution of the $O=Ti^{(IV)}$ TSPP. Consequently the LDH environment affects the energies of the two highest occupied molecular orbitals (HOMOs) of the $O=Ti^{(IV)}$) TSPP, $a_{1u}$ and $a_{2u}$, producing a mixed orbital character. Being consistent with these electronic structural changes of $O=Ti^{(IV)}$ TSPP in LDH, both the fluorescence spectral change and the fsdiffuse reflectance transient measurements imply that the photoexcitation of the $O=Ti^{(IV)}$ TSPP intercalated into LDH undergoes fast relaxation to the O=Ti(IV) $TSPP^+-LDH^- $charge transfer (CT) state within a few picoseconds, followed by a photoinduced electron transfer between the O=Ti(IV) TSPP and LDHs with a rate constant greater than %1×10^{10}S^{-1}$. No evidence is found for back electron transfer. In conclusion, the $O=Ti^{(IV)}$ TSPP intercalated LDH seems to be a possible candidate for an artificial reaction center for an efficient solar energy conversion system.

• Progress in Superconductivity
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• v.9 no.1
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• pp.50-55
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• 2007

We have installed a 61-channel magnetocardiography (MCG) system inside a magnetically shielded room (MSR) with a size of $2.4\;m\;{\times}2.4\;m\;{\times}2.4\;m$. The MCG system consists of 1st-order axial gradiometers containing double relaxation oscillation SQUIDs (DROSs) with pick-up coils of a base line of 70 mm. The MSR holds a shielding factor of 50 at 0.1 Hz and 10000 at 100 Hz, when its door in the middle on a front wall is closed. On opening the MSR door, we have obtained the characteristics of the MCG system with a 2.9 Hz noise generated from an air conditioning unit at 13 m distance off the MSR. In an open-door MSR ($140^{\circ}$ opening), a noise at the center channel increases up to $700\;fT/Hz^{l/2}$ at 2.9 Hz and $1.7\;pT/Hz^{1/2}$ at 60 Hz. MCG signals for a healthy human do not show distortion until the door opens to $45^{\circ}$, but show the effect of noise when the door opens further at $90^{\circ}$ and $140^{\circ}$. With the door opens to $45^{\circ}$, MCG measurement can be performed with ease of door operation and without creating claustrophobia for the patient.

• Progress in Superconductivity
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• v.10 no.2
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• pp.144-148
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• 2009

A current limiter was manufactured using a Josephson junction array to cut off an excessive current flowing into the SQUID sensor. The Fabricateed Josephson junction array was connected in series with a flux transformer that consists of a pick-up coil and an input coil, and the flux transformer was inductively coupled with a Double Relaxation Oscillation SQUID(DROS). The flux-voltage modulation curve was induced by applying an AC magnetic field whose magnitude was far smaller than that of the DC magnetic field. A change in the flux-voltage modulation curve of the SQUID was observed while the DC magnetic field was increased, to qualitatively examine the current limiting characteristic of the Josephson junction array. As a result, it was found that the SQUID flux-voltage modulation curve disappeared at the critical current of the Josephson junction array, which indicates that the Josephson junction array properly works as a current limiter.

• Progress in Superconductivity
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• v.10 no.2
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• pp.139-143
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• 2009

We have fabricated a low-noise 61-channel axial-type first-order gradiometer system for measuring fetal magnetocardiography(MCG) signals. Superconducting quantum interference device(SQUID) sensor was based on double relaxation oscillation SQUID(DROS) for detecting biomagnetic signal, such as MCG, magnetoencphalogram(MEG) and fetal-MCG. The SQUID sensor detected axial component of fetal MCG signal. The pickup coil of SQUID sensor was wound with 120 ${\mu}m$ NbTi wire on bobbin(20 mm diameter) and was a first-order gradiometer to reject the environment noise. The sensors have low white noise of 3 $fT/Hz^{1/2}$ at 100 Hz on average. The fetal MCG was measured from $24{\sim}36$ weeks fetus in a magnetically shielded room(MSR) with shielding factor of 35 dB at 0.1 Hz and 80 dB at 100 Hz(comparatively mild shielding). The MCG signal contained maternal and fetal MCG. Fetal MCG could be distinguished relatively easily from maternal MCG by using independent component analysis(ICA) filter. In addition, we could observe T peak as well as QRS wave, respectively. It will be useful in detecting fetal cardiac diseases.

• Journal of Genetic Medicine
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• v.1 no.1
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• pp.45-50
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• 1997

Neuroblastoma, a pediatric malignant neoplasm of neural crest origin, has a wide range of clinical virulence. The mechanisms contributing to the development of neuroblastomas are largely unclear, but non-random chromosomal changes identified over the past years suggest the involvement of genetic alterations. Amplification of the human N-myc proto-oncogene is frequently seen either in extrachromosomal double minutes or in homogeneously staining regions (HSRs) of aggressively growing neuroblastomas. N-myc maps to chromosome 2 band 24, but HSR have never been observed at this band, suggesting transposition of N-myc during amplification. We have constructed and analyzed the region-specific painting probe for HSR in neuroblastoma IMR-32 to determine the derivative chromosomes. Microdissection was performed on HSR using an inverted microscope with the help of microglass needles and an micromanipulator. We pretreated the microdissected fragments with Topoisomerase I which catalyzes the relaxation of supercolled DNA, and performed two initial rounds of DNA synthesis with T7 DNA polymerase followed by conventional PCR to enable the reliable preparation of Fluorescent in situ hybridization probe from a single microdissected chromosome. With this method, it was possible to construct the region-specific painting probe for HSR. The probe hybridized specifically to the HSRs of IMR-32, and to 2p24, 2p13 of normal chromosome. Our results suggest there was coamplification of N-myc together with DNA of the chromosome 2p24 and 2p13. Moreover, the fluorescent signals for the amplified chromosomal regions in IMR-32 cells were also easily recognized at a Thus this painting probe can be applied to detect the similar amplification of N-myc in neuroblastoma tissue, and the probe pool for HSR may be used to identify the cancer-relevant genes.

• Progress in Superconductivity
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• v.7 no.1
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• pp.46-51
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• 2005

We have developed control electronics to operate flux-locked loop (FLL), and analog signal filters to process FLL outputs for 64-channel Double Relaxation Oscillation SQUID (DROS) magnetocardiography (MCG) system. Control electronics consisting of a preamplifier, an integrator, and a feedback, is compact and low-cost due to larger swing voltage and flux-to-voltage transfer coefficients of DROS than those of dc SQUIDs. Analog signal filter (ASF) serially chained with a high-pass filter having a cut-off frequency of 0.1 Hz, an amplifier having a gain of 100, a low-pass filter of 100 Hz, and a notch filter of 60 Hz makes FLL output suitable for MCG. The noise of a preamplifier in FLL control electronics is $7\;nV/{\surd}\;Hz$ at 1 Hz, $1.5\;nV/{\surd}\;Hz$ at 100 Hz that contributes $6\;fT/{\surd}\;Hz$ at 1 Hz, $1.3\;fT/{\surd}\;Hz$ at 100 Hz in readout electronics, and the noise of ASF electronics is $150\;{\mu}V/{\surd}\;Hz$ equivalent to $0.13\;fT/{\surd}\;Hz$ within the range of $1{\sim}100\;Hz$. When DROSs are connected to readout electronics inside a magnetically shielded room, the noise of 64-channel DROS system is $10\;fT/{\surd}\;Hz$ at 1 Hz, $5\;fT/{\surd}\;Hz$ at 100 Hz on the average, low enough to measure human MCG.

• Progress in Superconductivity
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• v.13 no.1
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• pp.18-23
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• 2011

We developed a four-channel first order gradiometer system to measure magnetoencephalogram for mice. We used double relaxation oscillation SQUID (DROS). The diameter of the pickup coil is 4 mm and the distance between the coils is 5 mm. Coil distance was designed to have good spatial resolution for a small mouse brain. We evaluated the current dipole localization confidence region for a mouse brain, using the spherical conductor model. The white noise of the measurement system was about 30 fT/$Hz^{1/2}$/cm when measured in a magnetically shielded room. We measured magnetic signal from a phantom having the same size of a mouse brain, which was filled with 0.9% saline solution. The results suggest that the developed system has a feasibility to study the functions of brain of small animals.

• 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.

• Progress in Superconductivity
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• v.8 no.2
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• pp.164-168
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• 2007

We developed a SQUID magnetometer based on Double Relaxation Oscillation SQUID(DROS) for measuring magnetocardiography(MCG). Since DROS provides a 10 times larger flux-to-voltage transfer coefficient than the conventional DC-SQUID, simple flux-locked loop electronics could be used for SQUID operation. Especially, we adopted an external feedback to eliminate the magnetic coupling with adjacent channels. When the DROS magnetometer was operated inside a magnetically shielded room, average magnetic field noise was about 5 $fT/^{\surd}Hz$ at 100 Hz. Using the DROS magnetometer, we constructed a multichannel MCG system. The system consisted of 61 magnetometers are arranged in a hexagonal structure and measures a vertical magnetic-field component to the chest surface. The distance between adjacent channels is 26 mm and the magnetometers cover a circular area with a diameter of 208 mm. We recorded the MCG signals with this system and confirmed the magnetic field distribution and the myocardinal current distribution.