• Investigative Magnetic Resonance Imaging
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• v.10 no.2
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• pp.108-116
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• 2006

Purpose : High-resolution spiral-scan imaging is performed at 3 Tesla MRI system. Since the gradient waveforms for the spiral-scan imaging have lower slopes than those for the Echo Planar Imaging (EPI), they can be implemented with the gradient systems having lower slew rates. The spiral-scan imaging also involves less eddy currents due to the smooth gradient waveforms. The spiral-scan imaging method does not suffer from high specific absorption rate (SAR), which is one of the main obstacles in high field imaging for rf echo-based fast imaging methods such as fast spin echo techniques. Thus, the spiral-scan imaging has a great potential for the high-speed imaging in high magnetic fields. In this paper, we presented various high-resolution images obtained by the spiral-scan methods at 3T MRI system for various applications. Materials and Methods : High-resolution spiral-scan imaging technique is implemented at 3T whole body MRI system. An efficient and fast higher-order shimming technique is developed to reduce the inhomogeneity, and the single-shot and interleaved spiral-scan imaging methods are developed. Spin-echo and gradient-echo based spiral-scan imaging methods are implemented, and image contrast and signal-tonoise ratio are controlled by the echo time, repetition time, and the rf flip angles. Results : Spiral-scan images having various resolutions are obtained at 3T MRI system. Since the absolute magnitude of the inhomogeneity is increasing in higher magnetic fields, higher order shimming to reduce the inhomogeneity becomes more important. A fast shimming technique in which axial, sagittal, and coronal sectional inhomogeneity maps are obtained in one scan is developed, and the shimming method based on the analysis of spherical harmonics of the inhomogeneity map is applied. For phantom and invivo head imaging, image matrix size of about $100{\times}100$ is obtained by a single-shot spiral-scan imaging, and a matrix size of $256{\times}256$ is obtained by the interleaved spiral-scan imaging with the number of interleaves of from 6 to 12. Conclusion : High field imaging becomes increasingly important due to the improved signal-to-noise ratio, larger spectral separation, and the higher BOLD-based contrast. The increasing SAR is, however, a limiting factor in high field imaging. Since the spiral-scan imaging has a very low SAR, and lower hardware requirements for the implementation of the technique compared to EPI, it is suitable for a rapid imaging in high fields. In this paper, the spiral-scan imaging with various resolutions from $100{\times}100$ to $256{\times}256$ by controlling the number of interleaves are developed for the high-speed imaging in high magnetic fields.

• Journal of Radiation Protection and Research
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• v.39 no.1
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• pp.21-29
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• 2014

A new cold neutron triple-axis spectrometer (Cold-TAS) was recently constructed at the 30 MWth research reactor, HANARO. The spectrometer, which is composed of neutron optical components and radiation shield, required a redesign of the segmented monochromator shield due to the lack of adequate support of its weight. To shed some weight, lowering the height of the segmented shield was suggested while adding more radiation shield to the top cover of the monochromator chamber. To investigate the radiological effect of such change, we performed MCNPX simulations of a few different configurations of the Cold-TAS monochromator shield and obtained neutron and photon intensities at 5 reference points just outside the shield. Reducing the 35% of the height of the segmented shield and locating lead 10 cm from the bottom of the top cover made of polyethylene was shown to perform just as well as the original configuration as radiation shield excepting gamma flux at two points. Using gamma map by MCNPX, it was checked that is distribution of gamma. Increased flux had direction to the top and it had longer distance from top of segmented shield. However, because of reducing the 35% of the height, height of dissipated gamma was lower than original geometry. Reducing the 35% of the height of the segmented shield and locating lead 10cm from the bottom of the top cover was selected. After changing geometry, radiation dose was measured by TLD for confirming tester's safety at any condition. Neutron(0.21 ${\mu}Svhr^{-1}$) and gamma(3.69 ${\mu}Svhr^{-1}$) radiation dose were satisfied standard(6.25 ${\mu}Svhr^{-1}$).

• Korean Journal of Soil Science and Fertilizer
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• v.19 no.4
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• pp.307-314
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• 1986

Cu(II) binding mechanisms with water soluble organic fractions (WSOF) extracted from an agricultural soil (W), a soil treated with sludge for 6 years ($WS_6$), a sludge-soil mixture incubated for one week ($WS_1$), and sewage sludge (SS) were studied by electron spin resonance (ESR) spectroscopy and potentiometric titrations. Cu(II)-WSOF complexes produced $g_{11}$ values which were larger than $g_{\perp}$ values, indicating that the coordination of Cu(II) complex was an elongated octahedron. At liquid $N_2$ temperature (77K), the Cu(II)-W complex showed an anisotropic ESR spectrum while the Cu(II)-SS complex showed an isotropic spectrum. These spectral results suggest that the oxygen donor ligands of W may form relatively strong bonds with $Cu^{2+}$ due to extensive chelation while ligands of SS may form little or no chelate bonds with $Cu^{2+}$. The ESR spectra of Cu(II)-SS complex also suggest that each of four in-plane ligands (e.g., $COO^-$, $H_2O$, $Cl^-$, etc.) may act independently as monodentate ligands. Oxygen donor ligands such as aromatic carboxyl groups were probably the major Cu(II) binding sites in W. Sulfonate, aliphatic carboxyl group, and N-containing ligands were probably the major binding sites in SS at pH 5. The Cu(II) complexation with N-containing groups increased as sludge was added to the soil. Much higher (6x) pyridine concentrations were required to displace W from Cu(II)-W complex as compared to the Cu(II)-SS complex.

• Journal of the Korean Chemical Society
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• v.24 no.5
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• pp.380-392
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• 1980

Six coordinate low spin iron(Ⅱ) complexes of vicinal-dioximes, [Fe$(DH)_2B_2$] and [Fe$(DH)_2$B(CO)]($(DH)_2$=$(CHDH)_2$(bis(1,2-cyclohexadinedioximato) bivalent anion), $(DPGH)_2$-(bis(diphenylglyoximato) bivalent anion), $(F{\alpha}DH)_2(bis(furil-{\alpha}-dioximato)$ bivalent anion); B = monodentate neutral nitrogen base), have been prepared and their physical properties have been investigated with respect to the effects of the equatorial ligands, $(DH)_2$. The order of ${\pi}$-acceptor CO stretching frequency for [Fe$(DH)_2$B(CO)] is $(F{\alpha}DH)_2$ > $(DPGH)_2$> $(CHDH)_2$, while non-${\pi}$-acceptor $NH_3$ stretching frequencies for [Fe$(DH)_2(NH_3)_2$] show the opposite order to that of CO, i.e., $(CHDH)_2$ > $(DPGH)_2$ > $(F{\alpha}DH)_2$. These infrared spectral data together with Fe-N (oxime) and Fe-N (oxime) and Fe-N (B) stretching frequency data suggest that the nitrogen atoms of $(CHDH)_2$ are more basic and poorer ${\pi}$-acceptors than the corresponding nitrogen atoms of $(DPGH)_2$ and $(F{\alpha}DH)_2$, respectively. It has been found from the electronic spectral data of [Fe$(DH)_2$] and [Fe$(DH)_2$B(CO)] that the energy of the charge transfer band from iron(Ⅱ) to $(DH)_2$ increases as the basicity of $(DH)_2$ increases.

• Investigative Magnetic Resonance Imaging
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• v.11 no.2
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• pp.95-102
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• 2007

Purpose: To acquire high-resolution spiral-scan images at higher magnetic field, high homogeneous magnetic field is needed. Field inhomogeneity mapping and in-vivo shimming are important for rapid imaging such as spiral-scan imaging. The rapid scanning sequences are very susceptible to inhomogeneity. In this paper, we proposed a higher-order shimming method to obtain homogeneous magnetic field. Materials and Methods: To reduce measurement time for field inhomogeneity mapping, simultaneous axial/ sagittal, and coronal acquisitions are done using multi-slice based Fast Spin echo sequence. Acquired field inhomogeneity map is analyzed using the spherical harmonic functions, and shim currents are obtained by the multiplication of the pseudo-inverse of the field pattern with the inhomogeneity map. Results: Since the field inhomogeneity is increasing in proportion to the magnetic field, higher order shimming to reduce the inhomogeneity becomes more important in high field imaging. The shimming technique in which axial, sagittal, and coronal section inhomogeneity maps are obtained in one scan is developed, and the shimming method based on the analysis of spherical harmonics of the imhomogenity map is applied. The proposed technique is applicable to a localized shimming as well. High resolution spiral-scan imaging was successfully obtained with the proposed higher order shimming. Conclusion: Proposed pulse sequence for rapid measurement of inhomogeneity map and higher order shimming based on the inhomogeneity map work very well at 3 Tesla MRI system. With the proposed higher order shimming and localized higher order shimming techniques, high resolution spiral-scan images are successfully obtained at 3 T MRI system.

• Journal of the Korean Magnetics Society
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• v.26 no.4
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• pp.115-118
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• 2016

We investigated the magnetocrystalline anisotropy of pure ${\alpha}^{{\prime}{\prime}}-Fe_{16}N_2$ by using full-potential linearized augmented plane wave method (FLAPW). A very high magnetic moment was obtained for Fe (4d) site due to the lattice expansion in the z-direction, while the magnetic moment of Fe (4e) and (8h) site were suppressed due to hybridization with neighboring N atom. The calculated spin magnetic moments for different Fe sites (4d, 4e and 8h) were in good agreement with previously reported values. Due to the tetragonal distortion, we found a very large uniaxial anisotropy constant of $0.58MJ/m^3$. Besides, a high value of magnetization of 1.76MA/m was obtained. In additon, the estimated coercive field and maximum energy product of 6.51 kOe and 71.7 MGOe were obtained for pure ${\alpha}^{{\prime}{\prime}}-Fe_{16}N_2$. This may suggest that the ${\alpha}^{{\prime}{\prime}}-Fe_{16}N_2$ can be utilized for potential rare-earth free permanent magnet material.

• Journal of the Korean Magnetics Society
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• v.18 no.5
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• pp.163-167
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• 2008

The electronic structure and magnetism of superlattice systems consisted of Heusler compound $Co_2MnSi$ (CMS) and zinc-blende MnAs (MA) are investigated by means of the all-electron full potential linearized augmented plane wave method within the generalized gradient approximation. Four superlattice systems are considered, that is CMS(m)/MA(n), where m and n, being either 2 or 4, denote the number of alternatingly arrayed layers of the compounds in a superlattice along [001] direction. From the calculated total magnetic moments as well as the total density of states, it is found that neither of the four systems is half-metallic. It is also found that the Mn atoms are antiferromagnetically coupled in the systems of CMS2/MA2 and CMS2/MA4. The total and atom-resolved density of states of the four superlattices are compared with those of the bulk $Co_2MnSi$ and MnAs, and the influences of the change in the systems symmetry on the magnetism and half-metallicity are discussed.

• Journal of the Korean Magnetics Society
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• v.19 no.6
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• pp.197-202
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• 2009

The property of soft magnetism for the Corning glass/non-buffer or buffer Ta/Conetic(NiFeCuMo)/Ta prepared by the ion beam deposition sputtering was studied. The effect of crystal property and post annealing treatment depending on the thickness of Conetic thin films was investigated. The coercivities of Conetic thin films with easy and hard direction along to the applying magnetic field during deposition were compared with each other. The coercivity and magnetic susceptibility of Ta(5 nm)/Conetic(50 nm) thin film were 0.12 Oe and 1.2 ${\times}\;10^4$, respectively. From these results, firstly, the Conetic thin film was more soft magnetism thin film than other one such as permalloy NiFe. Secondly, the usage of soft magnetism Conetic thin film for GMR-SV (giant magneoresistance-spin valve) or MTJ (Megnetic Tunnel Junction) structure in a low magnetic field can be possible.

• Journal of the Korean Magnetics Society
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• v.19 no.3
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• pp.113-119
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• 2009

$^{57}Fe_xCu_{1-x}O$(x = 0.0, 0.02) powders were prepared by sol-gel method and their crystallographic and magnetic hyperfine properties have been studied using X-ray diffraction and $M{\ddot{o}}ssbauer$ spectroscopy (MS). The crystal structure of the samples is found to be monoclinic without any secondary phases and their lattice parameters increase with increasing annealing temperature ($T_A$), which is attributed to an increase in oxygen-vacancy content. MS measurements at room temperature indicate that $Fe^{3+}$ ions substitute $Cu^{2+}$ sites and ferromagnetic phase grow with increasing $T_A$. Magnetic hyperfine and quadrupole interactions of $^{57}Fe_{0.02}Cu_{0.98}O$ ($T_A=500^{\circ}C$) in the antiferromagnetic state at 17 K have been studied, yielding the following results: $H_{hf}=426.94\;kOe$, ${\Delta}E_Q=-3.67\;mm/s$, I.S.=0.32 mm/s, ${\theta}=65^{\circ}$, ${\phi}=0^{\circ}$, and ${\eta}=0.6$.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.412-421
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• 2023

Ultrasound brain stimulation is spot-lighted by its capability of inducing brain cell activation in a localized deep brain region and ultimately treating impaired brain function while the efficiency and directivity of neural modulation are highly dependent on types of stimulus waveforms. Therefore, to optimize the types of stimulation parameters, we propose a cell-cultivable ultrasonic transducer having a series stack of a spin-coated polymer piezoelectric element (Poly-vinylidene fluoride-trifluorethylene, PVDF-TrFE) and a parylene insulating layer enhancing output acoustic pressure on a glass-coverslip which is commonly used in culturing cells. Due to the uniformity and high accuracy of stimulus waveform, tens of neuronal cell responses located on the transducer surface can be recorded simultaneously with fluorescence microscopy. By averaging the cell response traces from tens of cells, small changes to the low intensity ultrasound stimulations can be identified. In addition, the reduction of stimulus distortions made by standing wave generated from reflections between the transducers and other strong reflectors can be achieved by placing acoustic absorbers. Through the proposed ultrasound transducer, we could successfully observe the calcium responses induced by low-intensity ultrasound stimulation of 6 MHz, 0.2 MPa in astrocytes cultured on the transducer surface.