• Journal of the Korean Magnetics Society
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• v.2 no.3
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• pp.251-256
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• 1992

Artificial superlattices of Co/Pd were prepared by RF magnetron sputtering Multilayered structure and compositional modulation were analyzed with a side angle x-ray diffractometer. It has been found that expansion of Co lattice occured in this artificial superlattice due to the lattice mismatch between Co and Pd. Perpendicular magnetic anisotropy could be observed when the Co layer thickness became less than 8${\AA}$ and maximum coercivity of 2350 Oe could be obtained in [Co(2.5 ${\AA}$)/Pd(9.3 ${\AA})]_{50}$/Pd$(200\;{\AA})$ with a perfect squareness of magnetic hysteresis loop. Characteristic of perpendicular magnetic anisotropy in Co/Pd superlattices could be related to the expansion of Co lattice caused by Pd layer and it turned out that as the thickness of Pd layer increased, perpendicular magnetic anisotropy increased. The interface anisotropy energy and volume anisotropy energy were calculated to be 0.29 ergs/$cm^2$ and -$6.9{\times}10^6$ ergs/$cm^3$ respectively, which are consistent with the values reported elsewhere.

• Progress in Superconductivity and Cryogenics
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• v.20 no.1
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• pp.1-10
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• 2018

The improvement of critical current properties of $REBa_2Cu_3O_{7-x}$ (REBCO) coated conductors by introducing artificial pinning centers (APCs) is examined with respect to the field-angle anisotropy, high-field performance and relaxation property with time. Nano-rods along the c-axis introduced by PLD method and isotropic nano-particles introduced by TFA-MOD method are treated. The theoretical analysis is also shown to understand the effect of APCs quantitatively. The effects of superconducting layer thickness that influences the high-field performance and relaxation property are also discussed. It is shown that the upper critical field, which is another important factor to determine the high-field property, can be improved by introduction of APCs through electron scattering at interfaces with the superconducting matrix. The optimum critical current property can be obtained by properly designing the morphology and number density of APCs and the superconducting layer thickness.

• Journal of Soil and Groundwater Environment
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• v.25 no.1
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• pp.12-24
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• 2020

This study was conducted to examine an artificial recharge system, which was considered to be an alternative for securing additional groundwater resources in a high-density greenhouse region. An injection well with a depth of 14.0 m was placed in an alluvial plain of the zone. Eight monitoring wells were placed in a shape of dual circles around the injection well. Aquifer tests showed that the aquifer was comprised with high-permeable layer with hydraulic conductivities of 1.5×10^-3~2.4×10^-2 cm/sec and storage coefficients of 0.07~0.10. A step injection test resulted in a specific groundwater-level rising (Sr/Q) values of 0.013~0.018 day/㎡ with 64~92% injection efficiencies. Results of the constant-rate injection test with an optimal injection rate of 100 ㎥/day demonstrated an enormous storage capacity of the alluvial aquifer during ten experimental days. To design an optimal recharge system for an artificial recharge, the high-permeable layer should be isolated by dual packers and suitable pressure should be applied to the injection well in order to store water. An anisotropy ratio of the alluvial aquifer was evaluated to be approximately 1.25 : 1 with an anisotropy angle of 71 degrees, indicating intervals among injection wells are almost the same.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.111-120
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• 2008

The characteristic of induced anisotropy is investigated in this study for the Pohang mudstone involving the cut plane discontinuity. The uniaxial and triaxial compression tests are performed for anisotropic rocks with artificial joint to look into anisotropic strength characteristics. Both the uniaxial compressive strength and triaxial compressive strength show the lowest value at the angle of cut plane, ${\beta}=30^{\circ}$ and the shoulder type of anisotropy is obtained. Anisotropy ratio (Rc) in uniaxial compression measures 9.0, whereas Rc=1.29-1.98 in triaxial compression is appeared. A series of analyses are made with the test results to derive the suitable parameter values when it is applied to the Ramamurthy (1985) failure criterion. The result of uniaxial compression test is analyzed by introducing the n-index into Ramamurthy failure criterion. The result shows that, n=l is suitable for ${\beta}=0^{\circ}{\sim}30^{\circ}$ and n=3 is suitable for ${\beta}=30^{\circ}{\sim}90^{\circ}$. To analyze the result of triaxial compression test by Ramamurthy failure criterion, anisotropy ratio in uniaxial compression test is added to Ramamurthy's equation and material constants are estimated by modified Ramamurthy's equation. When these values are applied back to Ramamurthy failure criterion, the predicted values are well fitted to the test results. And strength anisotropy for failure criteria of Jaeger (1960), McLamore & Gray (1967) and Hoek & Brown (1980) are also investigated.

• Journal of the Korean Geotechnical Society
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• v.16 no.1
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• pp.75-81
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• 2000

The anisotropy of soils has an important effect on stress-strain behavior. In this study, an attempt has been made to implement artificial neural network model for modeling the stress-strain relationship and predicting the undrained shear strength of normally consolidated clay with varying consolidation pressure ratios. The multi-layer neural network model, adopted in this study, utilizes the error back-propagation loaming algorithm. The artificial neural networks use the results of undrained triaxial test with various consolidation pressure ratios and different effective vertical consolidation pressure fur learning and testing data. After learning from a set of actual laboratory testing data, the neural network model predictions of the undrained shear strength of the normally consolidated clay are found to agree well with actual measurements. The predicted values by the artificial neural network model have a determination coefficient$(r^2)$ above 0.973 compared with the measured data. Therefore, this results show a positive potential for the applications of well-trained neural network model in predicting the undrained shear strength of cohesive soils.

• Journal of the Korean Geotechnical Society
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• v.19 no.3
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• pp.15-22
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• 2003

The appropriate description of the stress-anisotropy and time-dependent behavior of cohesive soils is very important in representing the real soil behavior. In this study, two constitutive relations have been incorporated based on the generalized viscous theory: one is the plastic constitutive relation adopted to capture the stress-anisotropy with a few model parameters; the other is the rate-dependent constitutive relation adopted to describe the strain rate-dependent behavior, an important time-dependent behavior in cohesive soils. The incorporated and proposed constitutive model has relatively a few model parameters and their values need not to be re-evaluated at different strain rates. The proposed model has been verified and investigated with the anisotropic triaxial test results obtained by using the artificial homogeneous specimens.

• Carbon letters
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• v.1 no.2
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• pp.76-81
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• 2000

Physical properties of artificial graphite electrodes were evaluated along three different directions; circumferential (X), radial (Y), and axial (Z) directions. Four kinds of commercial electrode products were used in this study for the evaluation; pole (AP) and nipple (AN) of manufacturer A, pole (BP) and nipple (BN) of manufacturer B. The mechanical, electrical, and thermal properties in X and Y directions were very similar to each other. In Z direction, however, the mechanical properties, including flexural strength and compressive strength, were higher, and electric resistance and thermal expansion were much lower than those in the other directions. The microstructures observed by optical microscope and scanning electron microscope revealed that the differences in properties by the measuring direction were caused by the preferential alignment of needle cokes along the Z direction. When comparing the properties of the electrode samples in the same direction, the mechanical properties mainly depended on the bulk density or porosity of the samples as well as preferential alignment of needle cokes.

• Korean Journal of Materials Research
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• v.23 no.2
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• pp.149-153
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• 2013

Delamination crack detection is very important for improving the structural reliability of laminated composite structures. This requires real-time delamination detection technologies. For composite laminates that are reinforced with carbon fiber, an electrical potential method uses carbon fiber for reinforcements and sensors at the same time. The use of carbon fiber for sensors does not need to consider the strength reduction of smart structures induced by imbedding sensors into the structures. With carbon fiber reinforced (CF/) epoxy matrix composites, it had been proved that the delamination crack was detected experimentally. In the present study, therefore, similar experiments were conducted to prove the applicability of the method for delamination crack detection of CF/polyetherethereketone matrix composite laminates. Mode I and mode II delamination tests with artificial cracks were conducted, and three point bending tests without artificial cracks were conducted. This study experimentally proves the applicability of the method for detection of delamination cracks. CF/polyetherethereketone material has strong electric resistance anisotropy. For CF/polyetherethereketone matrix composites, a carbon fiber network is constructed, and the network is broken by propagation of delamination cracks. This causes a change in the electric resistance of CF/polyetherethereketone matrix composites. Using three point bending specimens, delamination cracks generated without artificial initial cracks is proved to be detectable using the electric potential method: This method successfully detected delamination cracks.

• Journal of Magnetics
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• v.11 no.4
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• pp.182-188
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• 2006

The search for high-density recording materials has been one of most active and vigorous field in the field of magnetism. $FePt-L1_{0}$ nanoparticle has emerged as a potential candidate because of its high anisotropy. In this paper, we provide an overview of recent work at Argonne National Laboratory that contributes to the ongoing dialogue concerning the relation between structure and properties of the FePt nanoparticle system. In particular we discuss the ability to control structure and properties via dosing with Cr. Cr-dosed FePt films were grown via molecular beam epitaxy and annealed at $550^{\circ}C$ in an ultrahigh vacuum chamber, and were studied with the surface magneto-optic Kerr effect (SMOKE), scanning electron microscopy (SEM) and x-ray magnetic circular dichroism (XMCD). We found that small dosage of Cr helps to generate $L1_{0}$ phase FePt magnetic nanoparticles with small size, defined shape and regular spatial distribution on MgO (001) substrate. The nanostructures are ferromagnetic with high magnetic coercivity (${\sim}0.9T$) and magnetic easy axis in the desired out-of-plane orientation. We also show that controlling the lateral region where nanostructures exist is possible via artificial patterning with Cr.

• Carbon letters
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• v.15 no.2
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• pp.142-145
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• 2014

Isotropic synthetic graphite scrap and phenolic resin were mixed, and the mixed powder was formed at 300 MPa to produce a green body. New bulk graphite was produced by carbonizing the green body at $700^{\circ}C$, and the bulk graphite thus produced was impregnated with resin and re-carbonized at $700^{\circ}C$. The bulk density of the bulk graphite was $1.29g/cm^3$, and the porosity of the open pores was 29.8%. After one impregnation, the density increased to $1.44g/cm^3$ while the porosity decreased to 25.2%. Differences in the pore distribution before and after impregnation were easily confirmed by observing the microstructure. In addition, by using an X-ray diffractometer, the degrees-of-alignment (Da) were obtained for one side perpendicular to the direction of compression molding of the bulk graphite (the "top-face"), and one side parallel to the direction of compression molding (the "side-face"). The anisotropy ratio calculated from the Da-values obtained was 1.13, which indicates comparatively good isotropy.