• Information and Communications Magazine
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• v.24 no.2
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• pp.64-73
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• 2007

Recently, cross-layer design approach has been greatly attracting researchers' attention as an alternative for improving the performance of wireless data networks. The main reason why cross-layer approaches are particularly well suited for wireless networks is that there exists direct coupling between physical layer and upper layers. Therefore, with cross-layer approach, the protocol designers try to exploit the interaction between layers and promote adaptability at all layers, based on information exchange between layers. In this article we focus on the cross-layer engineering for high data-rate mobile Internet services through cellular networks. First, the general considerations in cross-layer engineering are outlined. Then, we discuss the common approach in literatures, which mainly deals with adaptability in physical and medium access control layer. Finally, we show that the cross-layer engineering taking account of all layers is more adequate for the mobile Internet services cellular network.

• Journal of Korea Foundry Society
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• v.22 no.2
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• pp.89-96
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• 2002

This study examined the effects of adding Zn to Sn-3.5Ag solder on the microstructure changes and behavior of interface reaction of the solder joint with Cu substrate. The solder/Cu joints were examined with microscope to observe the characteristics of microstructure changes and interfacial reaction layer with aging treatment for up to 120 days at $150^{\circ}C$. Results of the microstructure changes showed that the microstructures were coarsened with aging treatment, while adding 1%Zn suppresses coarsening microstructures. The Sn-3.5Ag/Cu had a fast growth rate of the reaction layer in comparison with the Sn-3.5Ag-1Zn at the aging temperature of $150^{\circ}C$. Through the SEM/EDS analysis of solder joint, it was proved that intermetallic layer was $Cu_6Sn_5$ phase and aged specimens showed that intermetallic layer grew in proportion to $t^{1/2}$, and the precipitate of $Ag_3Sn$ occur to both inner layer and interface of layer and solder. In case of Zn-containing composite solder, $Cu_6Sn_5$ phase formed at the side of substrate and Cu-Zn-Sn phase formed at the other side in double layer. It seems that Cu-Zn-Sn phase formed at solder side did a roll of banrier to suppress the growth of the $Cu_6Sn_5$ layer during the aging treatment.

• Geomechanics and Engineering
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• v.7 no.4
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• pp.355-374
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• 2014

An analytical solution of the fully coupled system of equations governing the plane strain deformation of a poroelastic medium with anisotropic permeability and compressible fluid and solid constituents is obtained. This solution is used to study the consolidation of a poroelastic clay layer with free permeable surface resting on a rough-rigid permeable or impermeable base. The stresses and the pore pressure are taken as the basic state variables. Displacements are obtained by integrating the coupled constitutive relations. The case of normal surface loading is discussed in detail. The solution is obtained in the Laplace-Fourier domain. Two integrations are required to obtain the solution in the space-time domain which are evaluated numerically for normal strip loading. Consolidation of the clay layer and diffusion of pore pressure is studied for both the bases. It is found that the time settlement is accelerated by the permeability of the base. Initially, the pore pressure is not affected by the permeability of the base, but has a significant effect, as we move towards the bottom of the layer. Also, anisotropy in permeability and compressibilities of constituents of the poroelastic medium have a significant effect on the consolidation of the clay layer.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.415-418
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• 1995

This paper describes a new technique for thickness measurement of a very thin layer less than one-quarter of the wavelength of ultrasonic wave using ultrasonic pulse-echo method. The technique determines the thickness of a thin layer in a layered medium form the amplitudes of the total reflected waves from the back side layer of interst. Thickness of a very thin layer few inch deep inside the media can be measured without using a very high frequency ultrasonic transducer over 100MHz which must be used in the conventional techniques for the precision measurement of a thin layer. The method also requires no inversion process to extract the thickness from the waveform of the reflected waves, so that it makes possible on-line measurement of the thickness of the layer.

• Bulletin of the Korean Chemical Society
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• v.16 no.12
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• pp.1229-1232
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• 1995

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.6
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• pp.579-582
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• 2012

Removing residual water in a fuel cell is a critical operational process for managing its performance and controlling its lifetime. Understanding the mechanism of water transport in fuel cells is essential for the design of the water removal process. In this study, an experimental method for measuring the water evaporation rate through a gas diffusion layer, which is a porous medium, under steady-state conditions was developed. Experimental bench tests were conducted to apply the developed method. Then, the effects of various parameters of the drying gas and the gas diffusion layer were experimentally measured. The water evaporation rate increased as the humidity of the drying gas decreased and the flow rate of the drying gas increased. In addition, a thinner gas diffusion layer yielded a higher water evaporation rate.

• Journal of Bio-Environment Control
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• v.13 no.3
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• pp.125-129
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• 2004

This study was conducted to identify the growth characteristics of melon cultivated with mixture medium of scoria and perlite in capillary system. The growth and fruit characteristics of all cultivars cultivated under the nutrient solution capillary supplying system were comprehensively favorable. Fresh fruit weight of the three cultivars was similar to weight criterion (1.8 - 2.0 kg/fruit) of melon. In melon of non-net type ‘Aris’ there were no differences in fruit characteristics between nutrient solution supply methods, but total soluble solid (TSS) was higher in drip and capillary systems showing $15.6^{\circ}$Brix and 15.5$^{\circ}$Brix, respectively, than that of mist spray system showing $14.4^{\circ}$Brix. In melon of net type, ‘Earl's elite’, drip and capillary systems showed better fruit characteristics and higher values of TSS compared to mist spray system. The change in pH in the medium before and after melon cropping was not significant between systems, but the pH of upper layer within medium in all system was higher than that of lower layer. The mineral content within lower layer showed higher value than that of the upper layer in drip system, but reversed in capillary system.

• Proceedings of the Botanical Society of Korea Conference
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• 1987.07a
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• pp.213-237
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• 1987

In vitro flowering system may minimize the confounded influence of non-floral meristem parts of plants in studying the relationship of a given treatment and flowering responses. We have induced flower buds from plantlets regenerated from zygotic embryo-derived somatic embryos of ginseng, which circumvented the normal 2-year juvenile period before flowering. The result suggests that the adulthood of ginseng root explants in the experiment previously conducted by Chang and Hsing (1980; Nature 284: 341-342) is not prerequired to flowering of plantlets regenerated through somatic embryogenesis. We have also induced flower buds from elongated axillary brandches from cotyledonary nodes by culturing ginseng zygotic embryos, seedlings, and excised cotyledonary nodes. It was found that 6-benzyladenine (BA) supplemented to the medium was essential for flowering, whereas abscisic acid (ABA) was inhibitory. Gibberellic acid(GA3) was also required for flowering when ABA was present with BA in the medium. The results suggest that cytokinins, gibberellins, and inhibitors play primary, permissive, and preventive roles, respective-ly, in the induction of flowering of ginseng. Tran Thanh Van (1980; Int. Rev. Cytol., Suppl. IIA: 175-194) has developed the "thin cell layer system" in which the induction of shoots, roots, or flower buds from epidermal layer explants were controlled by culture conditions and exogenous growth regulators in the medium, Utilizing the thin cell layer system, Meeks-Wagner et al. (1989; The Plant Cell 1: 25-35) have cloned genes specifically expressed during floral evocation. However, the system is too tedious for obtaining a sufficient amount of plant materials for biochmical and molecular biological studies of flowering. We have developed a garlic callus culture system and one obvious advantaging over the thin cell layer system is that an abundant cells committed to develope into flower buds proliferate. When the above cells were compared by two-dimensional gel electrophoresis with those which have just lost the competence for developing into flower buds, a few putative proteins specific to floral evocation were detected. The garlic callus culture system can be further explored for elucidation of the molecular biological mechanism of floral evocation and morphogenesis.hogenesis.

• Journal of the Korean Geophysical Society
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• v.4 no.1
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• pp.11-20
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• 2001

Seismic refraction and electrical resistivity surveys were conducted in Bangeosan Maaebul site located in Haman, Kyungnam, in order to present geophysical safety analysis method for masonry cultural properties. Seismic refraction exploration revealed that the ground was composed of three layers in term of seismic wave velocity; the upper, medium, and lower layers. The low velocity ranging from 308 to 366 m/sec in upper layer suggests weathered soil, the intermediate velocity from 1906 to 2090 m/sec in the medium layer indicates weathered rocks, and the high velocity from 5061 to 5650 m/sec in the lower layer implies extremely hard rocks. Our seismic result suggests that the upper and medium layer around the Maaebul should be reinforced to support the construct. The result of electric resistivity survey shows that there exists a low resistivity zone, ranging from 131 to 226 Ohm-m, at the right side of the Maaebul with the direction of NE-NNE. This area is the weakness zone as it plays role of the underground water passage in rainy season.

• Journal of the KSME
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• v.16 no.1
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• pp.49-53
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• 1976

Groundwater flow in a two-layer aquifer is studied theoretically and experimentally. Nonlinear differential equations are independently linearized for the upper and the lower layer, and approximate solutions are obtained. Fine sands and coarse sands are used in experiments. For steady flow, theoretical solutions agrees excellently with experimental results For unsteady flow, however, agreement is not so good, because the experimental conditions do not match with theoretical assumptions.