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1
Content available remote

Tiling Spaces of Taylor-Socolar Tilings

100%
Lee J.
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vol. 126
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issue 2
508-511
EN
The Taylor-Socolar tiling has been introduced as an aperiodic mono-tile tiling. We consider a tiling space which consists of all the tilings that are locally indistinguishable from a Taylor-Socolar tiling and study its structure. It turns out that there is a bijective map between the space of the Taylor-Socolar tilings and a compact Abelian group of a Q-adic space (Q̅) except at a dense set of points of measure 0 in Q̅. From this we can derive that the Taylor-Socolar tilings have quasicrystalline structures. We make a parity tiling from the Taylor-Socolar tiling identifying all the rotated versions of a tile in the Taylor-Socolar tiling by white tiles and all the reflected versions of the tile by gray tiles. It turns out that the Taylor-Socolar tiling is mutually locally derivable from this parity tiling.
2
Content available remote

EPR Paradox Solved by Special Theory of Relativity

100%
Lee J.
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vol. 125
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issue 5
1107-1110
EN
This paper uses the special theory of relativity to introduce a novel solution to Einstein-Podolsky-Rosen paradox. More specifically, the faster-than-light communication is described to explain two types of EPR paradox experiments: photon polarization and electron-positron pair spins. Most importantly, this paper explains why this faster-than-light communication does not violate the special theory of relativity.
3
Content available remote

Structural Transformation of Minimal Spanning Trees in World Commodity Market

64%
Lee J., Nobi A.
Acta Physica Polonica A
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2018
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vol. 133
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issue 6
1414-1416
EN
We consider structural change of a world trade-flow network for different commodities from 1995 to 2013. A minimum spanning tree is generated from the trade flow data, and we investigate the hierarchical organization of the tree by changing the hub node. Only a few countries are the hub nodes for many of the commodities. We observed the structural transitions, from a chain-like tree (many countries are hub nodes) to a bi-starlike tree (only two countries are hub nodes). In the bi-starlike tree, China and Germany are the only two hub nodes.
4
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Sensitizing Effects of Ti Alloying Contents on Damage Behavior of Austenitic Stainless Steel Exposed to Ultrasonic Vibratory Cavitation

64%
Lee J., Kim S.
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EN
The cavitation damage characteristics of austenitic stainless steel with different concentrations of Ti were investigated. The microstructure of the alloys was observed with optical microscope to identify its correlation with cavitation resistance. Hardness of the alloys was measured to examine its contribution to cavitation damage. It was found that the microstructure played a more significant role in cavitation damage behavior of austenitic stainless steel with Ti than the hardness. The findings in this study revealed that Ti addition in austenitic stainless steel may present either a beneficial or detrimental effect on cavitation damage behavior, depending on the microstructural characteristics. In particular, Ti content of 1.0% represented the most deteriorated cavitation characteristics due to the formation of relatively coarse precipitates. Therefore, control of Ti concentration is essential for marine application of austenitic stainless steel.
5
Content available remote

SiO_x Nanowires Produced on Molybdenum-Coated Si Substrates

51%
Kim H., Lee J., Yang J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
1017-1020
EN
We synthesized SiO_x nanowires with diameters of 30-140 nm, for the first time by the simple heating of the Mo-coated Si substrates. X-ray diffraction, selected area electron diffraction, and energy-dispersive X-ray spectroscopy indicated that the nanowires were in an amorphous state, comprising Si and O only. Fitting the photoluminescence spectrum with Gaussian functions revealed that the nanowires exhibited significant photoluminescence intensities near blue and green light regions. We extensively discussed the possible growth mechanism of SiO_x nanowires.
6
Content available remote

Microstructure Evolution of Tungsten-Based ODS Alloys Reinforced with the γ(Ni,~Fe) Phase by a Secondary Ball Milling Method

51%
Chen C., Zeng Y., Lee J.
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vol. 126
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issue 4
907-911
EN
In the current study, W-5Ni-2Fe-Y_2O_3 model alloys were produced using a high-energy planetary ball mill. The presence of the γ(Ni, Fe) phase is favored with respect to material properties in this alloy. Therefore, a secondary ball milling method was introduced to obtain a fine and uniformly distributed γ(Ni, Fe) phase. Phase development of mechanical alloyed powders was investigated by X-ray diffraction. The results show that the formation of the γ(Ni, Fe) phase was found after 18 h of a pre-milling procedure. A further secondary milling method produced a uniform microstructure with grain refinement. TEM results also show changes in the lattice parameters of the tungsten and γ(Ni, Fe) phase associated with the solid solubility limits in the alloy produced by secondary ball milling.
7
Content available remote

Influence of Applied Frequency on Microstructural and Electrochemical Characteristics of Ceramic Coating Produced on Al-Mg Alloy by Pulsed Plasma Electrolytic Oxidation

51%
Lee J., Lee S., Kim S.
Acta Physica Polonica A
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2016
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vol. 129
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issue 4
753-758
EN
Plasma electrolytic oxidation (PEO) coating is gaining attention as a promising surface treatment technique for lightweight metals and alloys such as Al, Mg and Ti. The coating involves complex interactions among various process parameters including substrate composition, current modes and electrolyte composition. In this study, ceramic coating was produced in silicate based alkaline solution on Al-Mg alloy by pulsed PEO with different applied frequencies (100, 500, 1000, 2000 Hz). The resultant coating was characterized using FE-SEM, EDS and HR-XRD. The electrochemical characteristics of the PEO coating were also investigated in seawater solution. It was found that changing frequency in the PEO process had a prominent effect on both surface and cross-sectional morphology of the coating. The electrochemical studies indicated that the pulsed PEO have improved the corrosion resistance of the Al-Mg substrate. In particular, the applied frequency of 100 Hz has produced one order of magnitude lower corrosion current density than that of the Al-Mg substrate.
8
Content available remote

Variable-Focus Fluid Lens Using an Electromagnetic Actuator

45%
Lee J., Park K., Choi J., Kim H., Kong S.
Acta Physica Polonica A
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2013
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vol. 123
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issue 2
202-204
EN
A variable-focus fluid lens controlled by an electromagnetic actuator and its characteristics are presented in this paper. The repulsive force between an NdFeB magnet and a solenoid through electromagnetic induction causes deflections in the elastomeric membranes integrated in the lens resulting in a focal-length change. The controllability of the focal length of the fabricated lens with an aperture size of 2 mm was approximately from infinity to 15 mm (with input current of 100 mA). The actuator including the solenoid was carefully designed to avoid thermal crosstalk of the lens fluid and magnet from the electromagnetic induction of the solenoid. The settling time to form a convex shape of the lens membrane was approximately 2.5 ms at an input current of 20 mA.
9
Publication available in full text mode
Content available

XANES Study of La_{0.75-x}Gd_xCa_{0.25}MnO_{3-δ} Solid Solutions

45%
Drozd V., Pęka̶a M., Liu R., Lee J., Chen J.
Acta Physica Polonica A
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2006
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vol. 109
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issue 4-5
583-589
EN
A series of solid solutions La_{0. 75-x}Gd_xCa_{0.25}MnO_{3-δ} with 0.0≤x≤0.75 was prepared via carbonate precursor precipitation method. Final sintering was performed at 1250ºC in oxygen flow atmosphere. The samples obtained were characterized by scanning electron microscope, X-ray diffraction measurements. Oxygen stoichiometry was analyzed by iodometric titration method. X-ray absorption spectroscopic methods of Mn L-edge and Mn K-edge X-ray absorption near edge structure were used to study oxidation state of manganese in the solid solutions and elucidate features of their local crystal structure. Orthorhombic crystal structure characteristics of the solid solutions were refined by Rietveld method. An increase in oxygen deficiency and average manganese oxidation state were found to accompany Gd concentration increase in La_{0.75-x}Gd_xCa_{0.25}MnO_{3-δ}. These results are consistent with Mn L-edge X-ray absorption near edge structure spectra, where a gradual change of Mn oxidation state with Gd concentration increase was detected. Origins of oxygen deficiency La_{0.75- x}Gd_xCa_{0.25}MnO_{3-δ} are discussed in terms of structural disorder caused by Gd substitution for La.
10
Content available remote

Structure, Morphology, and Band Gap of Ti-V-O Mixed Oxides Processed by Coprecipitation and Calcination

45%
Park M., Lim Y., Sung Y., Kwak D., Lee J.
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EN
Mixed oxides of Ti-V-O were co-precipitated by wet process using TiCl₄ and VOCl₃ as starting materials. As-precipitated gels were calcinated at 800°C for 4 hours in oxygen atmosphere. Effects of vanadium content on the structural evolution, morphology, and band gap of Ti-V-O oxides were investigated. Calcination has produced mixtures of TiO₂/VO₂/V₂O₅ oxides and has allowed formation of Ti_{1-x}V_{x}O₂. Lattice parameters of rutile TiO₂ were precisely measured to investigate vanadium substitution into single rutile phase of Ti_{1-x}V_{x}O₂ with varying vanadium content. As vanadium addition was increased, particles were coarsening rapidly during calcination. Band gap of the Ti-V-O oxides was measured using ultraviolet visible light spectrometer. A decrease of band gap down to 1.7 eV with the addition of maximum of 10 at.% of vanadium was measured, which is due to the formation of single phase of Ti_{1-x}V_{x}O₂ as well as the formation of metallic VO₂ or V₂O₅ particles.
11
Content available remote

Evaluation of Surface Characteristics and Physical Properties on Biodegradable Magnesium-Calcium Alloys by Anodic Oxidation

39%
Kim J., Lee J., Yang H., Park S., Lim H., Oh G., Yun K.
Acta Physica Polonica A
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2016
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vol. 129
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issue 4
736-741
EN
The purpose of this study was to determine the effect of calcium (Ca) on the surface characteristics and physical properties of magnesium-calcium alloys after anodization. A novel binary alloy Mg-xCa (in which x=0.5, 1, or 5 wt.%) was cast by combining magnesium (99.9%) and calcium (99.9%) in an argon gas (99.99%) atmosphere. A magnesium alloy rod having a diameter of 15 mm was cut into discs, each 2 mm thick. The specimens were subjected to anodic oxidation at 120 V for 15 minutes at room temperature in an electrolyte solution consisting of calcium gluconate, sodium hexametaphosphate, and sodium hydroxide. Surface and cross-sectional morphological changes were observed using scanning electron microscopy, and the microstructures and phases were detected by means of X-ray diffraction. Hardness and surface roughness were assessed by means of a Vickers hardness tester and a surface roughness meter, respectively. The results show that the physical properties of these magnesium-calcium alloys have been improved, because it was possible to control the dissolution rate according to the amount of calcium added.
12
Content available remote

Biological Evaluation of Anodized Biodegradable Magnesium-Calcium Alloys

33%
Kim J., Lee J., Lee K., Park S., Lim H., Park C., Bae J., Yun K.
Acta Physica Polonica A
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2016
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vol. 129
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issue 4
728-735
EN
The objective of this study was to evaluate the biocompatibility of studied binary magnesium-calcium (Mg-Ca) alloys for biodegradable intraosseous implants. Mg is necessary for health and is a non-toxic biodegradable material that decomposes naturally in the body. Nevertheless, Mg has been implicated in problems including diminished physical properties and corrosion resistance when degradation is too rapid prior to bone healing. This study has explored the effect of Ca on the corrosion resistance and biological evaluation after anodizing treatment with different contents of Ca alloy. Binary Mg-0.5Ca, Mg-1Ca and Mg-5Ca alloys were prepared by the casting method under an argon atmosphere and cut into disc-shaped pieces. Pure Mg alloy was used as the control. Anodic oxidation was performed for 15 minutes at a voltage of 120 V using an electrolyte solution containing Ca gluconate, sodium hexametaphosphate, and sodium hydroxide at room temperature. Corrosion resistance was analyzed using a corrosion tester. After a hydrogen evolution test, the surface pattern and phase changes were observed on a scanning electron microscop (SEM) and energy dispersive spectroscop (EDS). Microscopic evaluation of the adhesion and cell biological functions of Mg was conducted by observing the response of human fetal osteoblastic 1.19 cells with regard to changes in surface film properties, depending on the amount of Ca. Our results support the view that in Mg-xCa alloys (x=0.5, 1, 5 wt.%) treated using anodic oxidation, the increasing Ca content controls the rate of decomposition and improves corrosion resistance.
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