• Journal of Communications and Networks
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• 제18권1호
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• pp.1-7
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• 2016

Most of the previous proxy re-encryption schemes rely on the average-case hardness problems such as the integer factorization problems and the discrete logarithm problems. Therefore, they cannot guarantee its security under quantum analysis, since there exist quantum algorithms efficiently solving the factorization and logarithm problems. In the paper, we propose the first proxy re-encryption scheme based on the hard worst-case lattice problems. Our scheme has many useful properties as follows: Unidirectional, collusion-resistant, noninteractive, proxy invisible, key optimal, and nontransitive.We also provided the formal security proof of the proposed scheme in the random oracle model.

• 한국재료학회지
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• 제28권11호
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• pp.663-670
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• 2018

H13 tool steels are widely used as metallic mold materials due to their high hardness and thermal stability. Recently, many studies are undertaken to satisfy the demands for manufacturing the complex shape of the mold using a 3D printing technique. It is reported that the mechanical properties of 3D printed materials are lower than those of commercial forged alloys owing to micropores. In this study, we investigate the effect of microstructures and defects on mechanical properties in the 3D printed H13 tool steels. H13 tool steel is fabricated using a selective laser melting(SLM) process with a scan speed of 200 mm/s and a layer thickness of $25{\mu}m$. Microstructures are observed and porosities are measured by optical and scanning electron microscopy in the X-, Y-, and Z-directions with various the build heights. Tiny keyhole type pores are observed with a porosity of 0.4 %, which shows the lowest porosity in the center region. The measured Vickers hardness is around 550 HV and the yield and tensile strength are 1400 and 1700 MPa, respectively. The tensile properties are predicted using two empirical equations through the measured values of the Vickers hardness. The prediction of tensile strength has high accuracy with the experimental data of the 3D printed H13 tool steel. The effects of porosities and unmelted powders on mechanical properties are also elucidated by the metallic fractography analysis to understand tensile and fracture behavior.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권12호
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• pp.6116-6132
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• 2017

The proxy re-encryption allows an intermediate proxy to convert a ciphertext for Alice into a ciphertext for Bob without seeing the original message and leaking out relevant information. Unlike many prior identity based proxy re-encryption schemes which are based on the number theoretic assumptions such as large integer factorization and discrete logarithm problem. In this paper, we first propose a novel identity based proxy re-encryption scheme which is based on the hardness of standard Learning With Error(LWE) problem and is CPA secure in the standard model. This scheme can be reduced to the worst-case lattice hard problem that is able to resist attacks from quantum algorithm. The key step in our construction is that the challenger how to answer the private query under a known trapdoor matrix. Our scheme enjoys properties of the non-interactivity, unidirectionality, anonymous and so on. In this paper, we utilize primitives include G-trapdoor for lattice and sample algorithms to realize simple and efficient re-encryption.

• 한국분말재료학회지
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• 제10권3호
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• pp.190-194
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• 2003

Thin Ag films deposited onto $SiO_2/Si$ substrates by DC magnetron sputtering and thereafter annealed ,it temperatures 100-50$0^{\circ}C$ are investigated by scanning tunneling and atomic forte microscopy. It is shown that the film surface topography and microstructure are considerably changed as a result of annealing. To provide a quantitative estimation of the surface topography changes of Ag films the surface fractal dimension was calculated. Elasticity and hardness of the films are studied by a nanoindentation technique. The films are found to have value of elastic modulus close to that of bulk silver while their hardness and yield stress are essentially higher.

• 한국주조공학회지
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• 제30권1호
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• pp.22-28
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• 2010

Metal foam is a porous or cellular structure material and representative property is a very high porosity. Foamed materials have very special properties such as sound, vibration, energy and impact absorption capacity. Especially this properties are widely used for safety demands of architecture, auto and aircraft industry. But metal foam need to increased its compression strength and hardness. This study were researched about Al-Si alloy foams with variation amount of Si contents for their fabrication and properties such as porosity, cell structure, microstructure and mechanical properties. The result are that the range of pore size is 2~4 $mm{\phi}$, the high porosity are 88%, high yield strength is 1.8MPa, the strain ratio is 60~70% and vickers hardness is 33.1~50.6.

• 한국주조공학회지
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• 제36권6호
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• pp.215-221
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• 2016

In a recent study, the microstructures and mechanical properties of AM80-xSn magnesium alloys with semi solid casting and hot extrusion process were investigated. With increasing Sn content, the amount of ${\beta}$(Mg2Sn) phase increased, while the ${\alpha}-Mg$ dendritic size decreased. The hardness was increased by the Mg2Sn as the Sn content increased. With increasing Sn content, permanent mold cast and semi solid cast AM80 Mg alloy showed less reduction of hardness and also of extruded AM80 Mg alloy after annealing. In the case of the mechanical properties, the extruded semi solid casting AM80 Mg alloy showed higher tensile strength and yield strength with increasing Sn content compared to the extruded permanent mold cast AM80 Mg alloy at room temperature.

• Journal of Ceramic Processing Research
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• 제13권spc2호
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• pp.328-331
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• 2012

With the recent development of super-precision optical instruments, camera modules for devices, such as portable terminals and digital camera lenses, are increasingly being used. Since an optical lens is usually produced by high-temperature compression molding methods using tungsten carbide (WC) alloy molding cores, it is necessary to develop and study technology for super-precision processing of molding cores and coatings for the core surface. In this study, Rhenium-Iridium (Re-Ir) thin films were deposited onto a WC molding core using a sputtering system. The Re-Ir thin films were prepared by a multi-target sputtering technique, using iridium, rhenium, and chromium as the sources. Argon and nitrogen were introduced through an inlet into the chamber to be the plasma and reactive gases. The Re-Ir thin films were prepared with targets having a composition ratio of 30 : 70, and the Re-Ir thin films were formed with a 240 nm thickness. Re-Ir thin films on WC molding core were analyzed by scanning electron microscope (SEM), atomic force microscope (AFM), and Ra (the arithmetical average surface roughness). Also, adhesion strength and coefficient friction of Re-Ir thin films were examined. The Re-Ir coating technique has received intensive attention in the coating processes field because of promising features, such as hardness, high elasticity, abrasion resistance and mechanical stability that result from the process. Re-Ir coating technique has also been applied widely in industrial and biomedical applications. In this study, WC molding core was manufactured, using high-performance precision machining and the effects of the Re-Ir coating on the surface roughness.

• 한국환경복원기술학회지
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• 제18권6호
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• pp.215-226
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• 2015

This study introduced food waste into re-vegetation base materials for surface loss recovery of carry-away highway cut slope. The object of this study is to derive the mixing ratio of food waste by conducting a test installation, monitoring, analysis and evaluation for recovery of carry-away highway cut slope. The following items were investigated and analyzed each experimental zone to draw mixing ratio of re-vegetation base materials and food waste : the physical and chemical properties of the vegetation base materials, soil-hardness, soil-humidity, left out and the collapsed point, established number of trees, species richness of grass species and tree species, coverage, pest status, and invasion of disturbance species. The re-vegetation method was evaluated by each experiment zone which has different mixing ratio. As a result, experiment zone A was rated 45 points out of 60 rating points as the best re-vegetation method. However, this study result has been derived from one construction and short-term monitoring. In order to derive the suitable and dependable mixing ratio, conducting an objective re-vegetation method evaluation and long-term experiment and monitoring is required.

• 열처리공학회지
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• 제30권5호
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• pp.215-221
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• 2017

The effect of austenitizing temperature on the degree of carbides re-solutionizing, mean graine size, hardness and the volume fraction of retaind austenite ($V_{\gamma}$) etc., has been studied by means of metallography, X-ray diffractometry and hardness measurement in STD 11 tool steel. As austenitizing temperature increases, the amount of alloying elements which is re-dissolved into matrix increases, resulting in increase of $V_{\gamma}$, due to the chemical stabilization of austenite. The Vickers hardness value decreases with increasing austenitizing temperature, which is attributed to grain size as well the volume fractions of $V_{\gamma}$ and carbides. Theoretical diffraction intensity of (200) ${\alpha}^{\prime}$, (211) ${\alpha}^{\prime}$ (200) ${\gamma}$ and (220) ${\gamma}$ peaks obtained by $CuK_{\alpha}$ chracteristics X-ray (${\lambda}=0.15429nm$) was calculated, and quantitative analysis of $V_{\gamma}$ could be carried out by X-ray diffraction method. The resultant value is well coincided with the value obtained by image analysis method. When the quenched specimen is tempered above $200{\sim}400^{\circ}C$ for 30 min, the transition carbides i.e., MC and $M_2C$ in the size of about 20 nm begin to precipitate at $300^{\circ}C$.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.287-287
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• 2017

The objective of this study was to evaluate difference of quality properties of between fresh cooked rice and re-heated cooked rice after retrogradation. Nine rice varieties raised by NICS were compared the properties of physicochemical, texture, sensory evaluation, toyo glossiness value, pasting properties. Among nine rice cultivars, the changes of weight and length-width ratio of after soaking as well as cooking showed how water absorbed in each rice granule. The amount of water absorption after soaking was highest in Wolback (semi-waxy), Hiami and lowest in Samgwang, Seonpum, Ilpum. After cooking, the amount of water absorption was high in Dasan 1 and Andabyeo, however low in Ilpum. In the length-width ratio after soaking, Wolback (semi-waxy cultivar) and Anda (indica cultivar) increase their volume relatively as their shape are while others increased more in length than width. Among cooked rice, the highest value of length-width ratio shows in Anda, Dasan1, Hiami and Seonpum, the Wolbak was similar to that of non-glutinous rice. After cooking, the others stored at $10^{\circ}C$ for 16 hours for retrogradation (imitated at convenience store). Then re-heated using by microwave. Pasting properties were considerably affected by storage temperature and periods of rice. The setback showed in the following order: Wolback (-92.25 RVU, the lowest retrogradation) < Seonpum (-35.20) < Chindle (-22.08) < Jungsanggold (-21.98). Toyo glossiness value of cooked rice showed in the following order: Chindle (82.40) > Samgwang (79.43) > Hiami (79.23). Sensory evaluation of re-heated rice of Jungsanggold, Samgwang, and Chindle were 78.97, 78.36, and 77.35, respectively. Hardness, elasticity, and toughness of re-heated rice ware increased compared to cooked rice, whereas cohesiveness was decreased. Hardness and elasticity is higher in Seonpum, Dasan1 and Hiami, toughness is higher in Jungsanggold, Samgwang and Wolbak. Cohesiveness of Jungsanggold and wolbak showed higher than others.