• Journal of Conservation Science
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• v.12 no.1 s.15
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• pp.15-25
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• 2003

It is well known that the salt in stoneworks impact on damage of stone by various methods. Various kind of salt is detected in high content in the black surface layer of stone monuments and it is required about origin and roles of salts on blackening to considerate. In this study have been investigated the characteristics of salt in the black crust of sandstone and limestone which used in historical monuments in Berlin, Germany. Salt was analyzed for cation by Atomic Absorption and Atomic Emission Spectroscopy and for anion by ion Chromatograph. The representative ions are $Ca^{2+}\;and\;SO_4^{-2}$ in all samples and the most obvious combinations was proved in calcium sulfate by statistical methods. Because gypsum was detected by X-ray diffraction analyses in the black crusts, this calcium sulfate was confirmed by 2 hydrate type. The probable origin of Ca is air particle in atmosphere around sandstone and calcite in mother rock in limestone, and that of S is polluted air and mortar which used as conservation works.

• Journal of Korean Society for Atmospheric Environment
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• v.20 no.6
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• pp.715-727
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• 2004

This study was carried out to evaluate non-smoker's exposure levels to environmental tobacco smoke (ETS) in the air of offices in urban areas. A total of 65 offices were selected from two large cities, i.e. Daegu and Daejeon. The field sampling was conducted repeatedly in summer (1999) and winter (1999～2000). The measured ETS markers included respirable suspended particles (RSP as PM$_{40}$ ), vapor and particulate phase ETS markers, including nicotine, 3-ethnyl pyridine (3-EP), ultraviolet absorbing particulate matter (UVPM), fluorescing particulate matter (FPM), and solanseol in ETS particles (SolPM). RSP was measured gravimetrically by a microbalance. The particle samples were then used for the determination of particulate ETS markers by HPLC, while vapor phase markers determined by GC/NPD. The analytical methods were validated for repeatability, linearity, detection limits, and duplication precision. The concentrations of RSP and other ETS markers were significantly higher in smoking offices than non-smoking offices. Despite the similar smoking strength in each office for different seasons, the concentration levels of ETS components appeared to be higher in winter than summer. The contributions of ETS to RSP concentrations based on SolPM, FPM, and UVPM methods were estimated to be in the range of 15.2 ～ 25.3% in smoking offices, whereas 2.4 ～ 15.9% in non-smoking offices. The cooling and heating types did not affect significantly the concentrations of RSP and other ETS markers. Finally, further research issues were suggested to obtain more scientific information on the non-smoker's exposure to ETS with respect to the frame of risk assessment..

• Korean Journal of Fisheries and Aquatic Sciences
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• v.52 no.6
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• pp.656-665
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• 2019

Environmental monitoring was conducted to identify the characteristics and patterns of sedimentary environments of tidal flats in 12 areas on the west coast of Korea. The habitat of the mud shrimp Upogebia major contained higher organic and mud contents compared to the habitat of the manila clam Ruditapes philippinarum. In particular, the mud content increased from 84.38% to 89.18% in the Seongam-4 area, where the mud shrimp and manila clam coexist, and the mean grain size exhibited a finer particle size, from 5.48 Φ to 5.80 Φ. In the mud shrimp habitat, the sediment mud content was > 60% and the mean grain size was > 5 Φ. Additionally, the mud shrimp only inhabited open coast tidal flat areas. The management of shellfish aquaculture farms by physical methods should be continued based on comparison of the sedimentary environments in the Boryeong and Seongam areas in response to the damage to the mud shrimp habitat.

• The Journal of Advanced Prosthodontics
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• v.12 no.4
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• pp.197-203
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• 2020

PURPOSE. The aim of this study was to evaluate the effect of multiple firings on the bond strength between yttriatetragonal zirconia polycrystals (Y-TZP) and 2 types of resin cements. MATERIALS AND METHODS. Sixty 3Y-TZP specimens (LAVA Frame Multi) were divided into 3 groups depending on the following firing procedures: (1) 2-firing cycles, (2) 5-firing cycles, (3) 10-firing cycles. Two samples from each group were investigated by using SEM to determine the morphological changes. All specimens were treated with 125 ㎛ airborne-particle abrasion and the surface roughness of each specimen was measured. The specimens from each firing group were then further divided into 2 subgroups (n = 9) to apply 2 types of resin cement (MDP-free resin cement: RelyX Unicem-RU, and MDP containing resin cement: Panavia F 2.0-PA). The shear bond strength (SBS) test was performed and failure types of all the debonded specimens were classified by using a stereomicroscope as adhesive, cohesive, and mixed. The statistical analysis of surface roughness and SBS data were performed by using 1-way ANOVA and 2-way ANOVA followed by Tukey-HSD tests (α=.05). Failure modes were calculated as a percentage for each group. RESULTS. The bond strength of RU and PA to the specimens obtained with 2 firings were not statistically different from each other (P=.1). However, the SBS values of PA were found to be significantly higher than RU for the specimens obtained with 5 and 10 firing cycles (P=.001 and P=.02, respectively). Surface roughness analysis revealed no statistical difference between groups (P=.2). The SEM analysis of samples fired 5- and 10- times showed irregularities and boundary loss in zirconia grains, and empty spaces between zirconia grains. CONCLUSION. The bond strength of PA cement was higher than that of RU to the zirconia subjected to repeated firings (5 and 10 firing cycles). When zirconia is subjected to multiple firings, using MDP-containing resin cement can be recommended.

• Journal of Powder Materials
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• v.27 no.3
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• pp.233-240
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• 2020

Nano-sized ZnSe particles are successfully synthesized in an aqueous solution at room temperature using sodium borohydride (NaBH₄) and thioglycolic acid (TGA) as the reducing agent and stabilizer, respectively. The effects of the mass ratio of the reducing agent to Se, stabilizer concentration, and stirring time on the synthesis of the ZnSe nanoparticles are evaluated. The light absorption/emission properties of the synthesized nanoparticles are characterized using ultraviolet-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, and particle size analyzer (PSA) techniques. At least one mass ratio (NaBH4/Se) of the reducing agent should be added to produce ZnSe nanoparticles finer than 10 nm and to absorb UV-vis light shorter than the ZnSe bulk absorption wavelength of 460 nm. As the ratio of the reducing agent increases, the absorption wavelengths in the UV-vis curves are blue-shifted. Stirring in the atmosphere acts as a deterrent to the reduction reaction and formation of nanoparticles, but if not stirred in the atmosphere, the result is on par with synthesis in a nitrogen atmosphere. The stabilizer, TGA, has an impact on the Zn precursor synthesis. The fabricated nanoparticles exhibit excellent photo-absorption/discharge characteristics, suggesting that ZnSe nanoparticles can be alloyed without the need for organic solutions or high-temperature environments.

• Elastomers and Composites
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• v.33 no.5
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• pp.370-376
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• 1998

Mechanical properties of PVC[poly(vinylchloride)] composites containing the dust from blast and converter (Kwangyang Iron Co.) were investigated as a function of dust content. Tensile strength is increased, when the blast dust is mixed with PVC to the extent of 8.83wt % and impact strength is not significantly changed. From these results, it is suggested that blast dust containing CaO, SiO, MgO, $A1_2O_3$ and metallugical particle is compatible with PVC. Thermogravimetric analysis(TGA) showed that residual weight(%) at temperature $600^{\circ}C$ increased with the amount of blast dust and differential scanning calorimetry(DCS) showed that the thermal stability of PVC composite was increased when the weight ratio of blast dust was 8.83wt % X-ray diffractometry measurement also showed their blends and structures.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.3
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• pp.263-268
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• 2020

The purpose of this study is to investigate the damping properties of polyurethane composites incorporating waste tire rubber powder and preplaced coarse aggregates. Four types of polyurethane-based composites were manufactured, and longitudinal impact tests were performed. And vibration signals in the time domain and frequency domain were measured and values of damping ratio for each specimen were calculated. Test results showed that the damping ratios of polyurethane composites, in which the amount of polyurethane was reduced by 10.6% and 21.2% through incorporation of rubber particles, were 8.4% and 4.6% lower than that of pure polyurethane. The damping ratio of the polyurethane composite produced in a similar manner to the prepact concrete production method was found to be 22% lower than that of pure polyurethane, however, the amount of polyurethane was reduced by 50% and the stiffness was 25.7 times higher than that of pure polyurethane.

• Geomechanics and Engineering
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• v.20 no.3
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• pp.191-205
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• 2020

Soil shear strength parameters play a remarkable role in designing geotechnical structures such as retaining wall and dam. This study puts an effort to propose two accurate and practical predictive models of soil shear strength parameters via hybrid artificial neural network (ANN)-based models namely genetic algorithm (GA)-ANN and particle swarm optimization (PSO)-ANN. To reach the aim of this study, a series of consolidated undrained Triaxial tests were conducted to survey inherent strength increase due to addition of polypropylene fibers to sandy soil. Fiber material with different lengths and percentages were considered to be mixed with sandy soil to evaluate cohesion (as one of shear strength parameter) values. The obtained results from laboratory tests showed that fiber percentage, fiber length, deviator stress and pore water pressure have a significant impact on cohesion values and due to that, these parameters were selected as model inputs. Many GA-ANN and PSO-ANN models were constructed based on the most effective parameters of these models. Based on the simulation results and the computed indices' values, it is observed that the developed GA-ANN model with training and testing coefficient of determination values of 0.957 and 0.950, respectively, performs better than the proposed PSO-ANN model giving coefficient of determination values of 0.938 and 0.943 for training and testing sets, respectively. Therefore, GA-ANN can provide a new applicable model to effectively predict cohesion of fiber-reinforced sandy soil.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.5
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• pp.510-519
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• 2013

In this study, the spray characteristics of a pressure swirl atomizer classified into a liquid sheet-type swirl nozzle for Urea-SCR system were investigated experimentally with the variation of injection pressure. The length to diameter ratio ($l_o/d$) of the nozzle was 3.1, and the swirler was set inside the nozzle tip to give injecting fluid angular momentum. The injection duration of the nozzle was controlled by PWM (pulse width modulation) modes. The development processes of the spray were imaged by a 2-D PIV system, and the change of spray angle was measured. The atomization characteristics, including axial velocity and SMD, were measured using a 2-D PDA system with the injection pressures at room temperature and ambient pressure conditions. As the experimental results, the injection pressure had a significant impact on the spray structure showing a different shape around the spray leading edge, and the smaller SMD was observed with increasing injection pressures, which was similar to that of the previous work.

• Clean Technology
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• v.14 no.1
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• pp.21-28
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• 2008

The properties of the dispersion of the red, green, and blue pigments were investigated for the manufacture of the millbase of LCD color filters. Their physical properties and viscosity were controlled to apply to the screen printing in order to substitute the existing photolithography method. The best dispersion properties were obtained with dispersant BYK-2000 and monomer EB-140. The millbase was pre-mixed at 500 rpm for 30 min, and dispersed at 4000 rpm for 5 - 6 hour by Torus Mill. The resulting particle sizes were $100{\sim}110\;nm$ for red, $50{\sim}70\;nm$ for green, and $60{\sim}80\;nm$ for blue. When the millbase viscosity was 200-300 cps in the low viscosity formulation, an efficient impact of the beads on pigments was achieved. The dispersion properties were confirmed from the rheological behavior and color characteristics.