• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.05a
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• pp.140-144
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• 2002

In this paper, the plastic zone size ahead of the crack tip of DENT specimen and the crack growth length under cyclic loading were measured by ESPI system. These results of the plastic zone size measured by ESPI system were compared with the plastic zone size proposed by Irwin. The results of tile crack growth length measured by it were also compared with them measured by the image analysis system. It is confirmed that it is possible to measure the plastic zone and crack growth length.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.360.1-360.1
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• 2016

Hydroxyapatite (Ca10(PO4)6(OH)2, HAP) particles have attracted a great deal of attention in biomedical fields due to their good biocompatibility, bioactivity and fairly broad applications as drug delivery, dental implant, bone cement, and etc. Thus, many researchers have made an effort to add new functionalities such as luminescence, drug delivery, and bone regeneration properties up to HAP powders by controlling their nanostructure as well as composition. In this research, the mesoporous strontium substituted HAP (Sr-HAP) microspheres were synthesized using a hydrothermal method. In this synthesis, aspartic acid monomers were utilized to form microsphere by controlling surface energy of HAP particles and Sr ions were substituted into Ca ion sites, which induced luminescence property in HAP powders. Moreover, the change in the amount of Sr substitution was found to influence the particle size, morphology, and concurrently surface area, which led to changing drug loading as well as drug release property. The amount of Sr influences the morphology, luminescent properties, particle size, surface area cell viability and drug loading property, which are investigated by SEM, TEM, XRD, FTIR, BET, XPS and in vitro test such as MTT assay and drug release test. In particular, the multifunctional Sr-HAP with molar ratios of 0.25 (Sr/(Ca+Sr)) possessed the strongest luminescent property as well as the superior drug loading and sustained release properties that were correspondent with large surface area and pore size. Our study indicates that the fabricated multifunctional Sr-HAP microspheres are quite useful for bone regeneration and drug delivery.

• Steel and Composite Structures
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• v.1 no.3
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• pp.269-282
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• 2001

In this paper the results of an experimental program devoted to the assessment of the cyclic behaviour of full scale, European type, beam-column subassemblages with welded connections are presented. Six tests (five cyclic and one monotonic) have been carried out on three different series of specimens, encompassing a total of eighteen tests. The three specimen series have been designed with the aim of defining the effect of the column size on the connection behaviour, under different applied loading histories. The tests have evidenced the effect of the column size and panel zone design and of the applied loading history on the cyclic behaviour and failure modes of the connections.

• Computers and Concrete
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• v.20 no.1
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• pp.1-10
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• 2017

This paper focuses on the mesh-size dependency in numerical simulations of reinforced concrete (RC) structures subjected to blast loading. A tensile failure criterion that can minimize the mesh-dependency of simulation results is introduced based on the fracture energy theory. In addition, conventional plasticity based damage models for concrete such as the CSC model and the HJC model, which are widely used for blast analyses of concrete structures, are compared with the orthotropic model that adopts the introduced tensile failure criterion in blast tests to verify the proposed criterion. The numerical predictions of the time-displacement relations at the mid-span of RC beams subjected to blast loading are compared with experimental results. The analytical results show that the numerical error according to the change in the finite element mesh size is substantially reduced and the accuracy of the numerical results is improved by applying a unique failure strain value determined by the proposed criterion.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.974-982
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• 1992

The atomizations of CWM slurry and water are done by a wheel atomizer which is designed and manufactured for this experiment. The variables of the experiment are the angle of vane, aspect ratio, particle loading and the mean size of coal particle distribution. The main purposes of the experiment are to know how the angle of vane and aspect ratio of vane influence the size distribution of CWM droplets. The experimental results say there are no appreciable effects on the mean size of CWM droplets from the change of loading of coal prticles in slurry. The mean size of coal particle in slurry, however, influence quite strongly the mean size of CWM droplets. The mean size of CWM droplets is quite strongly affected by the angle of vane. The size distribution of CWM droplets is controllable by the change of aspect ratio.

• Journal of KIISE:Databases
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• v.29 no.3
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• pp.193-206
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• 2002

In this paper, we design and implement an efficient bulk-loading algorithm for CIR-Tree. Bulk-loading techniques increase node utilization, improve query performance and reduce index construction time. The CIR-tree has variable size of internal node entries since it only maintains minimal dimensions to decriminate child nodes. This property increases fan-out of internal nodes and improves search performance. Even though several bulk-loading algorithms for multi/high-dimensional index structures have been proposed, we cannot apple them to CIR-tree because of the variable size of internal node entries. In this paper, we propose an efficient bulk- loading algorithm for CIR-tree that improves the existing bulk-loading algorithm and accomodates the property of CIR-tree. We also implement it on a storage system MiDAS-III and show superiority of our algorithm through various experiments.

• Structural Engineering and Mechanics
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• v.36 no.5
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• pp.575-598
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• 2010

The shape and size of the plastic zone around the crack tip are analyzed under pure mode I, pure mode II and mixed mode (I+II) loading for small scale yielding and for both plane stress and plane strain conditions. A new analytical formulation is presented to determine the radius of the plastic zone in a non-dimensional form. In particular, the effect of T-stress on the plastic zone around the crack tip is studied. The results of this investigation indicate that the stress field with a T-stress always yields a larger plastic zone than the field without a T-stress. It is found that under predominantly mode I loading, the effect of a negative T-stress on the size of the plastic zone is more dramatic than a positive T-stress. However, when mode II portion of loading is dominating the effect of both positive and negative T-stresses on the size of the plastic zone is almost equal. For validating the analytical results, several finite element analyses were performed. It is shown that the results obtained by the proposed analytical formulation are in very good agreements with those obtained from the finite element analyses.

• Journal of Pharmaceutical Investigation
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• v.30 no.4
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• pp.253-258
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• 2000

In order to design the oral vaccine delivery system, we prepared the alginate micro spheres containing GFP (green fluorescent protein) as a model drug by spray method. To optimize the preparation conditions of microspheres, we investigated the effects of various parameters including nozzle pressure, nozzle opening angle, and concentrations of sodium alginate and calcium chloride. The prepared microspheres were evaluated by measuring their sizes, loading efficiency, and morphology. The particle size of microspheres was affected by the concentration of sodium alginate and calcium chloride, nozzle pressure, and nozzle opening angle. As the concentration of sodium alginate increased, GFP loading efficiency and particles size of microsphere also increased. However, it was observed to be difficult to spray the sodium alginate solution with concentration greater than 1.5% (w/v), due to high viscosity. The pressure over $3\;kgf/cm^2$ didn't affect the size of particles. As a result, the spraying method enabled us to prepare microspheres for oral vaccine delivery system. In this study, microspheres prepared with 1% (w/v) sodium alginate had greater loading efficiency and better spherical shape.

• Structural Engineering and Mechanics
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• v.86 no.5
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• pp.607-619
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• 2023

This study, it was tried to evaluate the asphalt behavior under tensile loading conditions through indirect Brazilian and direct tensile tests, experimentally and numerically. This paper is important from two points of view. The first one, a new test method was developed for the determination of the direct tensile strength of asphalt and its difference was obtained from the indirect test method. The second one, the effects of particle size and loading rate have been cleared on the tensile fracture mechanism. The experimental direct tensile strength of the asphalt specimens was measured in the laboratory using the compression-to-tensile load converting (CTLC) device. Some special types of asphalt specimens were prepared in the form of slabs with a central hole. The CTLC device is then equipped with this specimen and placed in the universal testing machine. Then, the direct tensile strength of asphalt specimens with different sizes of ingredients can be measured at different loading rates in the laboratory. The particle flow code (PFC) was used to numerically simulate the direct tensile strength test of asphalt samples. This numerical modeling technique is based on the versatile discrete element method (DEM). Three different particle diameters were chosen and were tested under three different loading rates. The results show that when the loading rate was 0.016 mm/sec, two tensile cracks were initiated from the left and right of the hole and propagated perpendicular to the loading axis till coalescence to the model boundary. When the loading rate was 0.032 mm/sec, two tensile cracks were initiated from the left and right of the hole and propagated perpendicular to the loading axis. The branching occurs in these cracks. This shows that the crack propagation is under quasi-static conditions. When the loading rate was 0.064 mm/sec, mixed tensile and shear cracks were initiated below the loading walls and branching occurred in these cracks. This shows that the crack propagation is under dynamic conditions. The loading rate increases and the tensile strength increases. Because all defects mobilized under a low loading rate and this led to decreasing the tensile strength. The experimental results for the direct tensile strengths of asphalt specimens of different ingredients were in good accordance with their corresponding results approximated by DEM software.

• Fire Science and Engineering
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• v.30 no.2
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• pp.62-67
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• 2016

In this study, the optical depth is analyzed with the effects of droplet size distribution of the water curtain nozzle to attenuate the radiative heat transfer. The HELOS/VARIO equipment is used for the measurement of the droplet size distributions. The spray characteristics are quantified by the investigation of Deirmenjian's modified gamma distribution function. The distribution constant of the nozzle can be obtained as ${\alpha}=1$ and ${\gamma}=5.2$. The generalized equation of the optical depth related with the droplet size distribution is introduced. These results will be applicable to the analysis of the design condition of the water curtain nozzle.