• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.3
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• pp.102-109
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• 2002

The fatigue crack growth under mixed mode condition has been discussed within the scope of linear fracture mechanics such as maximum tangential stress, maximum tangential principal stress and minimum strain energy density. The purpose of this study is to investigate the characteristics of fatigue test crack growth in 304 stainless steel under mixed node. The fatigue test results carried out by using inclined pre-crack specimens was compared to both of the theoretical predictions of the criteria, maximum tangential stress and stain energy density. As difference from theoretical analysis, the transition region from mixed mode to mode I appeared in the fatigue test. There is deep relationship between the angle of slanted pre-crack and transition. Therefore, as applying the different stress intensity factor to each node I+II and mode I, the directions and rates of fatigue crack growth are evaluated more accurately under mixed mode.

• Journal of the Korean Chemical Society
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• v.23 no.1
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• pp.15-19
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• 1979

The new concept of the Bonding and Antibonding Regions in the transition density space is developed from the Integral Hellmann-Feynman Theorem and the positive definiteness of the transition density. The unility of this concept is fully demonstrated for H2 system. It is expected that the nature of the electronic perturbation energy due to the change of nuclear configuration can be successfully understood by using this concept. Properties of the transition density is briefly discussed.

• Journal of the Korean Graphic Arts Communication Society
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• v.21 no.1
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• pp.11-20
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• 2003

Equilibrium swelling curves of N-isopropyl acrylamide(NIPA) gel and its ionized copolymer gels were obtained as a function of temperature. Discontinuous volume changes of the gels were observed. Phase transition temperature was increased with the ionized counter parts of the gels. Equilibrium swelling of ionized copolymer gel cylinder was found to depend strongly on their diameters. Crosslinking density of NIPA gel was adjusted by increasing N,N'-methylenebisacrylamide(BIS). Phase transition temperature was increased with the crosslinking density.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.453-453
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• 2007

Electrodeless fluorescent lamp exhibit two modes of operation: a low density mode in which the power is capacitively coupled to the plasma and which is known as the E-mode, and a higher density mode which is an inductive discharge known as the H-mode. The transition between these two(E to H) mode exhibits hysteresis. It is observed that transition currents change at different frequencies and hysteresis exists not only between the starting and minimum maintaining currents of the electromagnetic mode (H mode) discharge but also between the starting and minimum maintaining currents of the electrostatic mode (E mode) discharge. Hysteresis effect can be important role in dimming system.

• Progress in Superconductivity
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• v.14 no.1
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• pp.34-38
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• 2012

The effect of graphene inclusion in the ex-situ $MgB_2$ was analyzed with the help of resistivity behavior and critical current density studies. Amount of graphene was systematically varied from 0% for pristine sample to 3% by the weight of $MgB_2$. Graphene that is considered as a good source of carbon was found to be intact without any significant carbon doping in $MgB_2$ structure as reveled by XRD measurements. There was no signature of graphene inclusion as far as the superconducting transition is concerned which remained same at 39 K for all the samples. The transition width being sensitive to defect doping remained more or less about 2 K for all the samples showing no variation due to doping. Although there was no change in the superconducting transition or transition width, the graphene doped sample showed noticeable decrease in the overall resistivity behavior with respect to decrease in temperature. The graphene inclusion acted as effective pinning centers which have enhanced the upper critical field of these samples.

• Progress in Superconductivity
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• v.11 no.2
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• pp.112-117
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• 2010

We examine phase transition of the spin density wave and $\pi$ phase shifted superconductivity in the Fe pnictide superconductors. The phase diagram is described in the plane of the temperature T and the doping x with the combination of Ginzburg-Landau expansion of the free energy near the multi-critical temperature $T_c$ and the self-consistent numerical iterations of the gap equations. The phase separation or coexistence is determined by computing the 4-th order terms of the free energy which is confirmed by the numerical calculations. We can show the phase coexistence when the spin density wave is incommensurate. And the first order phase transition is observed near the boundary between commensurate and incommensurate spin density wave.

• 전기의세계
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• v.30 no.7
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• pp.441-447
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• 1981

As a preceeding work for the study on dielectric characterstics of a kind of low density polyethylene introduced morphological change by mechanical method, glass transition temperature which is regarded as a macroscopic aspect for relaxation of molecular chain segments has been observed by means of temperature dependent dilatometric measurement. The origina specimen clearly shows two knees which correspond to two peaks (.gamma. and .betha. peak) in the intenal friction measurement, suggesting the existence of separated glass transition temperatures at 150.deg.k and 260.deg.k respectively. On the specimen irradiated to 100 Mrad both glass transition temperatures tend to shift towards high temperature sides because of crosslinking by irradiation. furthemore an evidence can be seen that radiation effect, even in amorphous phase, is also slelctive depending on slight morphological differences. The specimen extended to four times in length shows a peculiar nature such as negative linear thermal expansion coefficient increasing with temperature between 220.deg.k and ambient temperature and that this fact is interpreted by considering that c axis of the lattice aligns along the extended direction by drawing, further c axis inherently possesses the characteristics of negative linear thermal expansion coefficient. For the observations that the relatively small positive linear expansion on the specimen extended to ca. two times as well as the part below 220.deg.k of the specimen extended to four times, it is considered for the reason of the facts that the incompletely oriented region indicated as the middle part of Peterlin's model tends to restore partially to orginal arrangement-a kind of phase transition-as increasing with temperature.

• Bulletin of the Korean Chemical Society
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• v.24 no.6
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• pp.832-836
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• 2003

To extend the knowledge of triple bonding between group 6 transition metal and heavier group 14 elements, the structural and bonding aspects of ($η^5-C_5H_5$)$(CO)_2$M≡ER (M = Cr, Mo, W; E = Si, Ge, Sn, Pb) are investigated by hybrid density functional calculations at the B3PW91 level. Substituent effects are also investigated with R = H, Me, $SiH_3$, Ph, $C_6H_3-2,6-Ph_2$, $C_6H_3-2,6-(C_6H_2-2,4,6-Me_3)_2$, and $C_6H_3-2,6-(C_6H_2-2,4,6- iPr_3)_2$.

• Journal of Information Display
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• v.10 no.4
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• pp.143-148
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• 2009

The theoretical current density equations for organic semiconductors was derived according to the internal carrier emission equation based on the diffusion model at the Schottky barrier contact and the mobility equation based on the field dependence model, the so-called "Poole-Frenkel mobility model." The electric field becomes constant because of the absence of a space charge effect in the case of a higher injection barrier height and a lower sample thickness, but there is distribution in the electric field because of the space charge effect in the case of a lower injection barrier height and a higher sample thickness. The transition between the injection- and bulk-limited currents was presented according to the Schottky barrier height and the sample thickness change.

• Bulletin of the Korean Chemical Society
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• v.30 no.12
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• pp.2927-2929
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• 2009

The hydricities of d$^6$ metal hydride complexes in aqueous solution were calculated by using density functional theoretical (DFT) calculations coupled with a Poisson-Boltzmann (PB) solvent model. Hydricity describes the hydride donor ability of the metal-hydrogen bond, which assists in the study of the mechanism of many catalytic processes and chemical reactions that involve transition metal hydrides. The calculation scheme produced hydricity values that were in good agreement with experimental estimation. The inclusion of a water molecule as a weakly bound ligand to five-coordinate metal complexes gave an improved correlation result.