• Korean Journal of Materials Research
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• v.22 no.9
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• pp.450-453
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• 2012

In crystalline solar cells, the substrate itself constitutes a large portion of the fabrication cost as it is derived from semiconductor ingots grown in costly high temperature processes. Thinner wafer substrates allow some cost saving as more wafers can be sliced from a given ingot, although technological limitations in slicing or sawing of wafers off an ingot, as well as the physical strength of the sliced wafers, put a lower limit on the substrate thickness. Complementary to these economical and techno-physical points of view, a device operation point of view of the substrate thickness would be useful. With this in mind, BC-BJ Si and GaAs solar cells are compared one to one by means of the Medici device simulation, with a particular emphasis on the substrate thickness. Under ideal conditions of 0.6 ${\mu}m$ photons entering the 10 ${\mu}m$-wide BC-BJ solar cells at the normal incident angle (${\theta}=90^{\circ}$), GaAs is about 2.3 times more efficient than Si in terms of peak cell power output: 42.3 $mW{\cdot}cm^{-2}$ vs. 18.2 $mW{\cdot}cm^{-2}$. This strong performance of GaAs, though only under ideal conditions, gives a strong indication that this material could stand competitively against Si, despite its known high material and process costs. Within the limitation of the minority carrier recombination lifetime value of $5{\times}10^{-5}$ sec used in the device simulation, the solar cell power is known to be only weakly dependent on the substrate thickness, particularly under about 100 ${\mu}m$, for both Si and GaAs. Though the optimum substrate thickness is about 100 ${\mu}m$ or less, the reduction in the power output is less than 10% from the peak values even when the substrate thickness is increased to 190 ${\mu}m$. Thus, for crystalline Si and GaAs with a relatively long recombination lifetime, extra efforts to be spent on thinning the substrate should be weighed against the expected actual gain in the solar cell output power.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.27 no.6
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• pp.754-770
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• 1994

Suspended sediment distribution and water column processes in the upper Neuse River estuary, North Carolina, were monitored monthly from February 1988 through February 1989, in order to identify the turbidity maximum, to determine its temporal and spatial variation under changing conditions(freshwater runoff, wind, and tide). During most of the observation periods a weak turbidity maximum, associated with the estuarine circulation processes, developed at a flow convergence zone, near the upstream limit of salt intrusion. No turbidity maximum was found when the water column was vertically homogeneous with respect to salinity and when there was no consistent upstream bottom flow. Annual migration of the turbidity maximum, accompanied by migration of salt intrusion, was over 20 km of the upper estuary. Due to the coincidence of dominant wind direction(NE-SW) with the main orientation of the Pamlico-Neuse system, wind played the dominant role in dynamics of the turbidity maximum by influencing the degree of salinity stratification and the extent and strength of estuarine circulation. Tidal effects on the sediment dynamics were negligible.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.9
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• pp.740-746
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• 2013

Design with crashworthiness concept has been emphasized for almost aircraft and motor vehicles. However, crashes accompanied serious injury and death have been continuously occurred, and will be occurred subsequently. What was worse, it is a well-known fact that there were a good many crashes classified as survivable accidents in which fatal injuries were reported. But we cannot say that fatal injuries were inevitable consequences of those crashes. If crashworthy design for seat, restraint systems, and cabin strength were adequate or right, survivability in a crash event could be maximized greatly. To substantiate the right crashworthiness, we must thoroughly understand the characteristics of human tolerance under abrupt acceleration change, and the cabin design should be combined with proper use of energy absorbing technologies that reduce accelerations experienced by the occupants. In this paper, the emphasis on the human tolerance under abrupt accelerations as well as the necessity of change in design requirements for crash environment will be stressed to widen the belt of consensus for the right crashworthy design.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.2
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• pp.51-57
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• 1985

In the design of civil engineering structures, the designers are invariably faced to the uncertainties and the randomness of the design parameters such as material properties and loads. Even when the structures are built, the actual geometries of the structures are also subject to their random variations from their nominal design values. Thus, the reliability of a structure in terms of these uncertainties and variations becomes a matter of great concern to the structural designers. This study employs the First Order Second Moment Method to evluate numerically the reliability of a simple tension member and discusses the influence on the final failure probability of that structure due to: 1) use of equivalent normal distribution in place of non-normal distribution, 2) linearization of non linear limit state equation. A discussion is also made on the necessity of fundamental studies on the distrubution characteristics of the strength of locally produced construction materials and those of the loads frequently encountered in the structural design.

• Journal of Korea Soil Environment Society
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• v.5 no.1
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• pp.55-63
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• 2000

Bentonite has low hydraulic conductivity and high sorption capacity to limit hazardous heavy metals migration, and thus it has been considered as a liner material for the landfill of hazardous wastes. With a domestic bentonite sorption tests were carried out to investigate the adsorption isotherm and the effect of solution chemistry and temperature on adsorption. Freundlich isotherm was applied to fit the experimental data of lead adsorption, which fitted them well. Freundlich constants and correlation coefficient were calculated to be $K_{F}$\;=\;1.14$, n = 1.70, and $r^{2}\;=\;0.99$, respectively. The distribution coefficients($K_{d}$) for the adsorption of lead decreased with increasing initial lead concentration. The IL increased with increasing the pH of solution and sharply increased at pH > 7, which was attributed to the precipitation of lead species. The IL decreased with increasing the ion strength of solution. The $K_{d}$ gave a small increase with the concentration of ${SO_4}^{-2}$, whereas it had a nearly constant level with the concentration of ${HCO_3}^{-}$ in solution. An increase in the temperature of experimental solution increased the $K_{d}$.

• Journal of Korean Society of Steel Construction
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• v.25 no.3
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• pp.223-231
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• 2013

Recently, high-performance steels have been increasingly used for structural materials in buildings and bridges with the demand for high-rise and long-span of main structures. This paper offers a series of basic study for the design specification of structural members using high performance steel, that is material properties of HSA800 (High-performance rolled steel for building structures). Built-up square tube stub columns with variables of width-to-thickness ratios are planned as a parametric study in order to investigate the local buckling behaviors and check the current design limit of width-to-thickness ratio. In addition, the buckling behaviors of stub columns obtained finite element (FE) analysis were compared with those from experimental tests. The verified FE model was used for parametric study and checked applicability of high-strength steel on current design specification.

• Earthquakes and Structures
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• v.9 no.1
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• pp.127-143
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• 2015

In conventional seismic design, structures are assumed to be fixed at the base. To reduce the impact of earthquake loading, while at the same time providing an economically feasible structure, minor damage is tolerated in the form of controlled plastic hinging at predefined locations in the structure. Uplift is traditionally not permitted because of concerns that it would lead to collapse. However, observations of damage to structures that have been through major earthquakes reveal that partial and temporary uplift of structures can be beneficial in many cases. Allowing a structure to move as a rigid body is in fact one way to limit activated seismic forces that could lead to severe inelastic deformations. To further reduce the induced seismic energy, slip-friction connectors could be installed to act both as hold-downs resisting overturning and as contributors to structural damping. This paper reviews recent research on the concept, with a focus on timber shear walls. A novel approach used to achieve the desired sliding threshold in the slip-friction connectors is described. The wall uplifts when this threshold is reached, thereby imparting ductility to the structure. To resist base shear an innovative shear key was developed. Recent research confirms that the proposed system of timber wall, shear key, and slip-friction connectors, are feasible as a ductile and low-damage structural solution. Additional numerical studies explore the interaction between vertical load and slip-friction connector strength, and how this influences both the energy dissipation and self-centring capabilities of the rocking structure.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.4
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• pp.37-44
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• 2015

An experimental study was performed for the analysis of frequency-equivalence ratio correlation in the methane-air premixed flame influenced by ultrasonic standing wave. Evolutionary features of the propagating flame were caught by high-speed camera, and the variation of flame-behavior including local velocities was investigated in detail using a post-processing analysis of the high-speed images. It was found that propagation-velocity augmentation of the methane-air premixed flame by the intervention of ultrasonic standing wave was made in leaner mixture, but the velocity diminished when the strength of chemical reaction was saturated around the slightly fuel-rich side of stoichiometry.

• Journal of Pharmaceutical Investigation
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• v.20 no.3
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• pp.51-76
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• 1990

It is sometimes said lately that the pH of the human gastric juice is significantly different among individuals. Thus, the dissolution behavior of coated solid dosage forms should preferably be independent of the pH of the test solution. With these points as a background, the effect of pH on the dissolution velocity of coated tablets was studied to compare that of Pharmacoat with other gastric soluble film coating materials. Three viscosity types of Pharmacoat have been available(3, 6 and 15cP) until now. the 6cP type has been considered to be the most suitable for a tablet coating amongst the three types. The 3 cP type with a low degree of polymerization, is capable of providing high concentration, but the film strength is so inferior that sometimes cracking of the film may occur. On the other hand, in the case of the 15cP type, high polymer concentration cannot be achieved because of the high dgree of polymerization, and thus it is uneconomical for coating. Now, there is a strong demand to reduce the coating time even when HPMC is used in the 6cP type in order to reduce the coating cost. In order to improve this problem, we have concentrated our attention on reducing the viscosity value of HPMC to an allowable lower limit from 6cP. As a result of this study, it was found that the reduction of the viscosity value to around 4.5cP enabled the use of a higher solution concentration and an incidental shorter coating time without giving any substantial adverse effects on the properties of coated preparations. These experiment results are presented in the later part of this presentation. Based on this study, we have added the viscosity type of 4.5cP as one of the Pharmacoat products as Pharmacoat-645.

• International Journal of Highway Engineering
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• v.17 no.6
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• pp.37-45
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• 2015

PURPOSES : The purpose of this study is to validate the design criteria of the concrete modular road system, which is a new semi-bridge-type concept road, through a comparison of numerical analysis results and actual loading test results under static axial loads. METHODS : To design the semi-bridge-type modular road, both the bridge design code and the concrete structural design code were adopted. The standard truck load (KL-510) was applied as the major traffic vehicle for the design loading condition. The dimension of the modular slab was designed in consideration of self-weight, axial load, environmental load, and combined loads, with ultimate limit state coefficients. The ANSYS APDL (2010) program was used for case studies of center and edge loading, and the analysis results were compared with the actual mock-up test results. RESULTS : A full-scale mock-up test was successfully conducted. The maximum longitudinal steel strains were measured as about 35 and 83.5 micro-strain (within elastic range) at center and edge loading locations, respectively, under a 100 kN dual-wheel loading condition by accelerating pavement tester. CONCLUSIONS : Based on the results of the comparison between the numerical analysis and the full-scale test, the maximum converted stress range at the edge location is 32~51% of the required standard flexural strength under the two times over-weight loading condition. In the case of edge loading, the maximum converted stresses from the Westergaard equation, the ANSYS APDL analysis, and the mock-up test are 1.95, 1.7, and 2.3 times of that of the center loading case, respectively. The primary reason for this difference is related to the assumption of the boundary conditions of the vertical connection between the slab module and the crossbeam module. Even though more research is required to fully define the boundary conditions, the proposed design criteria for the concrete modular road finally seems to be reasonable.