Yoon B. Kim

HYDROGEN ABSORPTION AND DESORPTION BEHAVIOR IN PR-FE-B TYPE ALLOYS

In this study, the hydrogen absorption and desorption behavior of Pr–Fe–B type alloys with addition of Co, Ga, and Zr was investigated focusing on the disproportionation and recombination reaction in HDDR process. In Pr13B6Febal. alloy, the second hydrogen absorption reaction which corresponds to the disproportionation reaction in HDDR process occurs at about 620 °C, and the recombination reaction was not observed below 1000 °C in hydrogen atmosphere. In alloys with Co content of 12 at.%, the second hydrogen desorption reaction, which corresponds to the recombination reaction in HDDR process, occurs at about 955 °C and the occurring temperature of the recombination reaction is further decreased with increasing Co content. The Ga addition to Pr13B6Febal. alloy also reduces the recombination reaction temperature and has no significant influence on the disproportionation reaction. Moreover, the lowering of the recombination reaction temperature is remarkable when Ga and Co are added simultaneously. On the co...

Determination of mirodenafil and sildenafil in the plasma and corpus cavernous of SD male rats

The purpose of the present study was to determine sildenafil and a novel PDE-5 inhibitor, mirodenafil in the plasma and corpus cavernosum tissue of rats to compare their pharmacokinetic properties. The concentrations of mirodenafil and sildenafil in the rat plasma and corpus cavernosum tissue samples were analyzed using LC-MS/MS after a single oral administration at a dose of 40mg/kg to rats. Although the T(max), Tlambda(1/2) and MRT were not different between mirodenafil and sildenafil, the C(max) and AUC of mirodenafil were significantly higher than those of sildenafil in the plasma and corpus cavernosum tissue. Consequently mirodenafil remained longer than sildenafil in the plasma and tissue. This may provide pharmacokinetic evidence for assessment of the in vivo efficacy of mirodenafil and sildenafil.

Phases of melt-spun Sm1−xFe7+x alloys and magnetic properties of their nitrides

Sm1-xFe7+x (0 less than or equal to x less than or equal to 0.9) alloys were induction-melted and rapidly quenched at various wheel velocities of 20-50 m/s. The results of X-ray diffraction show that for the composition of 0 less than or equal to x less than or equal to 0.1 the rhombohedral Th2Zn17-type structure is the main phase, and for the composition of 0.2 less than or equal to x less than or equal to 0.9 the hexagonal TbCu7-type structure is formed. AC initial susceptibility experiments indicate that at annealing temperatures below 580 degrees C the amorphous phase is crystallized to the TbCu7-type phase, while annealing up to 800 degrees C the TbCu7-type phase is transformed to the Th2Zn17 phase. After nitrogenation, the optimal condition for the best magnetic properties is obtained in Sm12.5Fe87.5Ny, quenched at 50 m/s and annealed at 700 degrees C for 30 min, and consequently nitrogenated at 460 degrees C for 4 h. The best result for the coercivity H-i(c) of the Sm12.5Fe87.5Ny achieved is 18.9 kA/cm (23.7 kOe).

Fe-based nanocrystalline alloy powder cores with excellent high frequency magnetic properties

Toroidal shape FeSiBNbCu nanocrystalline alloy powder cores were prepared by compaction at room temperature after creating Cu-oxide layer as an insulator on the surface of FeSiBNbCu nanocrystalline alloy powder. The characteristics of the Cu-oxide layer and its effect on the high frequency magnetic properties of the compacted cores were investigated. A Cu-oxide layer was successively synthesized by electroless plating of Cu on the FeSiBNbCu nanocrystalline alloy powder and subsequent thermal oxidation. FeSiBNbCu nanocrystalline alloy powder core prepared from the powder having Cu-oxide layer exhibits a high value of quality factor and a stable permeability up to high frequency range over 10MHz. The core loss could be reduced remarkably and the dc-bias property could be improved significantly by synthesizing Cu-oxide layer on the FeSiBNbCu nanocrystalline alloy powder. Effective insulation by Cu-oxide layer between the FeSiBNbCu nanocrystalline alloy powder could be attributed to the improvement in high-fr...

LC–MS/MS method for determination of hederacolchiside E, a neuroactive saponin from Pulsatilla koreana extract in rat plasma for pharmacokinetic study

A simple, rapid, and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was applied to pharmacokinetic study of a neuroactive oleanolic-glycoside saponin, hederacolchiside E from SK-PC-B70M, a standardized extract of Pulsatilla koreana in rat. Rat plasma samples were pretreated by protein precipitation with acetonitrile, eluted from C(18) column, and analyzed using electrospray ionization (ESI)-MS/MS in negative ion mode. Digoxin was used as an internal standard. The standard curves were linear (r>0.997) over the concentration ranges of 2-500 ng/mL. The intra- and inter-day precisions were measured to be below 9% and accuracy between 90 and 111% for all quality control samples at 2, 20, 100, and 500 ng/mL (n=5). The lower limits of quantification (LLOQ) for hederacolchiside E was 2 ng/mL and the limit of detection (LOD) 0.5 ng/mL using 20 microL of plasma sample. Subsequently, hederacolchiside E was determined in rat plasma samples after oral administration of SK-PC-B70M. The mean maximum plasma concentrations of hederacolchiside E were 0.07, 0.13, and 0.36 microg/mL and the mean areas under the plasma concentration versus time curve 0.56, 1.27, and 6.46 microg h/mL at doses of 100, 200, and 400 mg/kg, respectively, which indicated non-linear pharmacokinetic pattern. In conclusion, this method was successfully applied to the pharmacokinetic study of hederacolchiside E after an oral administration of SK-PC-B70M to rats.

Vacuum hot pressing of Fe–Si–B–Nb-based amorphous powder cores and their high-frequency magnetic properties

FeSiBNb amorphous powder was prepared by gas atomization and subsequently consolidated into bulk amorphous cores by hot pressing after creating an oxide layer on the surface of the powder. FeSiBNb amorphous powders exhibiting a saturation magnetization of 127emu∕g and a coercivity of 0.34 Oe were successfully obtained by gas atomization. Hot pressing enabled consolidation of the FeSiBNb amorphous powder core within the supercooled liquid region. The core prepared from the FeSiBNb amorphous powder covered with an oxide layer of 1μm thickness showed excellent high-frequency characteristics with a stable permeability over 10 MHz and a core loss of 400mW∕cm3 at 50 kHz for Bm=0.1T. The oxide layer formed on the FeSiBNb amorphous powder was effective in improving the frequency dependence of magnetic properties and in reducing the core loss for the FeSiBNb amorphous powder cores.

Recrystallization behaviour of Al-2Li-3Mg-1Cu-0.12Zr-X Mn(X = 0, 0.5) alloy

Grain size control by thermo-mechanical treatment is investigated in aluminum-lithium alloys. Rolling and subsequent recrystallizing treatment have been widely employed to obtain a fine grained structure. Humphreys has reviewed the recrystallization process in particle containing alloys and proposed a new deformation zone model. He thought that subgrain size or dislocation density increased abruptly beyond the deformation and boundary. He considered that a recrystallization nucleus formed and grew fast within the deformation zone. For nucleation of new grains, the maximum misorientation within the deformation zone should be sufficient to form a high angle boundary in the matrix, and for continuous growth of the nucleus, the deformation zone should be larger than critical size R{sub cr}. In this work, the recrystallization behaviors of Mn-free and Mn-bearing Al-Li alloys at various recrystallization temperatures were investigated to confirm the deformation zone model proposed by Humphreys.

Hydrogen Permeation Properties of Pd-Coated Ni37.5Nb27.5Zr25Co5Ta5 Amorphous Membrane

The hydrogen permeation properties of the Pd-coated Ni37.5Nb27.5Zr25Co5Ta5 amorphous membranes have been investigated at 673 and 723K for 720 hours (1 month). Values of the hydrogen permeability during these long term tests were found to be reduced of about 50 and 30 % at 673 and 723K, respectively. The reduction in the hydrogen permeability could be correlated to the change in the composition of the coating as well as at the interface between Pd coating and Ni-based amorphous membrane.

Attenuation characteristics of near-field electromagnetic noise through microstrip line for magnetic absorbers with different levels of conductivity

Attenuation characteristics of near-field electromagnetic noise through microstrip line attached with electromagnetic thick films with different levels of electrical conductivity for frequencies in the range of 0.1–6GHz were investigated with numerical simulation via the three dimensional finite-element high-frequency structure simulator (HFSS) code. The electromagnetic absorption of the semiconducting magnetic or nonmagnetic films highly increased up to 80% at above 1GHz, while the absorption of the nonmagnetic conductor or the insulating films was significantly diminished. The remarkable enhancement in the loss factor of the semiconducting magnetic or nonmagnetic films was attributed to the increase in loss factor of the eddy-current loss. Even though the reflection of the semiconducting magnetic films at above 58S∕m was significantly lowered by the magnetic loss effect compared to that of the semiconducting nonmagnetic films, the reflection below 1GHz was still high enough to incur electromagnetic inte...

Adhesion properties of copper/polyimide film modified by reactive ion etching(RIE)

Surface modification of polyimide(PI) films was treated with oxygen RIE by varying ion doses from 1x1016 to 1x1018 ions/cm2 at an ion beam energy of 250 eV. Following the modification of PI surface, metal films consisting of NiCr/Cu and Cu were deposited on modified PI films by D.C. magnetron sputtering and electroplating, respectively. The surface modified PI film was characterized by XPS, AFM, SEM and contact angle measurement, respectively. The water contact angle of PI film decreased significantly from 64° to 4.4° with an increase of ion dose, indicating that the surface energy of PI film increased. The XPS spectrum showed that functional group, particularly C-O bonding, on modified PI surface was significantly increased by interaction between scissored unstable chains and reactive ions. The modified PI film surfaces by oxygen RIE showed significant improvement in adhesion to a overcoated metal film of NiCr/Cu.