• 한국미생물·생명공학회지
• /
• 제22권5호
• /
• pp.561-563
• /
• 1994

For the more effective isolation of soil actinomycetes, we have developed HHV (Hair hydrolysate-vitamin) agar medium, containing hair as the sole source of carbon and nitrogen. The HHV agar medium was superior to other media such as colloidal chintin agar, glycerol-arginine agar and starch-casein-nitrate agar, and HV (humic acid-vitamin) agar. The maximum effect of this medium has been shown in hair dry weight 0.4 g/l medium. Of each soil sample, the greatestest number of actinomycetes was isolated from the potato annual planted soil among the tested samp- les. The genus of actinomycetes isolated from the potato annual planted soil sample was identified such 5 group as Stretomyces, Micromonospora, Microbispora, Nocardia and Saccharopolyspora.

• 한국분말재료학회지
• /
• 제18권4호
• /
• pp.372-377
• /
• 2011

In this study, we reported the microstructure and properties of Ag-$SnO_2$ contact materials fabricated by a controlled milling process with subsequent consolidation. The milled powders were consolidated to bulk samples using a magnetic pulsed compaction process. The nano-scale $SnO_2$ phases were distributed homogeneously in the Ag matrix after the consolidation. The relative density and hardness of the Ag-$SnO_2$ contact materials were 95~96% and 89~131 Hv, respectively.

• Restorative Dentistry and Endodontics
• /
• 제24권1호
• /
• pp.233-239
• /
• 1999

Recently, a second generation composite resin system(ceromer) was introduced with significantly improved mechanical properties. The purpose of this study was to compare a ceromer with the other restorative materials and to assess its clinical usefulness. In this study, we used four restorative materials : amalgam (BESTALOY$^{(R)}$), indirect composite resin (Clearfil CR Inlay$^{(R)}$), ceromer (Targis$^{(R)}$) and ceramic (Vintage$^{(R)}$). And then we devided into four groups. The materials of each group were as follows : Amalgam group : BESTALOY$^{(R)}$ (Dong Myung Dental Industrial Co.) Composite Resin group : Clearfil CR Inlay$^{(R)}$ (Kuraray) Ceromer group : Targis$^{(R)}$ Dentin (Ivoclar-Vivadent) Ceramic group : Vintage$^{(R)}$ (Shofu Inc.) According to the above classification, we made samples through the polymerization of BESTALOY$^{(R)}$, Clearfil CR Inlay$^{(R)}$ and Targis$^{(R)}$ with separable cylindrical metal mold and firing of Vintage$^{(R)}$ in a investment mold. And then, we measured and compared the value of compressive strength, diametral tensile strength and Vicker's microhardness of each sample. The results were as follows : 1. Amalgam showed the highest value of compressive strength (390.37${\pm}$42.22MPa) and the value of ceromer was somewhere between ceramic and indirect composite resin. There were significant differences among the experimental groups(p<0.001). 2. Indirect composite resin showed the highest value of diametral tensile strength (74.21${\pm}$15.33MPa) and there was no significant difference with ceromer. Ceromer was higher diametral tensile strength than amalgam and ceramic (p<0.001). 3. Ceramic showed the highest value of microhardness (538.44${\pm}$37.38Hv) and the value of ceromer was somewhere between ceramic and indirect composite resin. There were significant differences among the experimental groups (p<0.001).

• Journal of Biosystems Engineering
• /
• 제39권1호
• /
• pp.11-20
• /
• 2014

Purpose: Walking type cultivator used for weeding generated excessive handle vibration as well as bouncing motion depending on the weeding speed. This research was conducted to define a design factor of the rotary weeding blades for reducing soil reaction forces as well as hand vibration. Methods: The motion and forces acting on the rotary blades were reviewed to find out the most influencing parameter on hand vibration. The installation angle (IA) of the blade was selected and analyzed to determine the condition of no reaction force less. For removing the unnecessary upward soil reaction, the design factor theory of weeding blade was suggested based on geometrics and dynamics. For evaluation of design factor theory, the experiment in situ was performed base on ISO 5349:1. The vibration $a_{hv}$ and theoretical value $X_{MF}$ were compared with two groups that one was positive group ($X_{MF}$ > 0) and the other was negative group ($X_{MF}$ < 0). Results: $X_{MF}$ was derived from rotational velocity, forward velocity, disk diameter, weeding depth, blade's width and IA of blade. Two groups had significant difference (p < 0.05). In aspect of the group mean total exposure duration, positive group was 17.53% bigger than negative group. When disk radius 100, 150 and 200 mm, minimum IAs were $4{\sim}27^{\circ}$, $3{\sim}15^{\circ}$ and $2{\sim}10^{\circ}$, respectively. A spread sheet program which calculated XMF was developed by Excel 2013. Conclusions: According to this result, minimum IA of weeding blade for soil reaction reduction could be obtained. For reduction hand-arm vibration and power consumption, minimum IA is needed.

• 대한치과보철학회지
• /
• 제47권4호
• /
• pp.424-434
• /
• 2009

연구목적: 임플란트는 수직교합 하중에는 비교적 잘 견디나 측방하중에 대해서는 약한 역학적 성질을 갖고 있으므로 임플란트의 재료 특성과 기하학적 형태에 따른 응력 분석 연구의 필요성이 제기되고 있다. 연구재료 및 방법: 외부육각구조를 갖는 28개의 임플란트를 7개씩 4군으로 나누어 그 제품에 적합한 UCLA gold abutment를 이용해, 제3형 금합금으로 보철 물을 제작하였고, A군 (3i, FULL $OSSEOTITE^{(R)}$-Implant), B군 (Nobelbiocare, Branemark $System^{(R)}$Mk III Groovy RP), C군 (Neobiotec, $SinusQuick^{(TM)}$ EB), D군 (Osstem, US-II)으로 분류하였다. 고정체와 지대주나사, 지대주를 연결한 후 수직적으로 절단하여 연마한 후 미세경도계를 이용하여 10군데에서 경도측정을 실시하였고, 동적하중 피로시험기를 이용하여 60-600 N범위로 파절시까지 동적 하중을 가하였다. 주사전자현미경을 이용하여 지대주나사 및 고정체의 파절 양상과 파절 위치 등을 관찰하였고, 유한요소분석을 통해 고정체와 지대주 나사에 나타나는 응력 분포와 파절면을 비교 분석하였다. 결과: 1.고정체 경도는 A, B, C, D군에서 각각 245.3, 289.7, 281.3, 300.4 Hv로 D군이 가장 높았고, A군이 가장 낮았다. 지대주 나사의 경도는 A, B, C, D군에서 각각 340.00, 317.62, 306.5, 306.2 Hv로 A군이 가장 높고, D군이 가장 낮았다. 2. 모든 실험군에서 임플란트 고정체의 파절은 응력이 집중되는 고정체 3-4번째 나사산 홈 (valley) 부위 또는 내면의 사공간부와 일치하는 부위에서 발생되었고, 피로수명은 A, B, C, D군에서 각각 31585, 47311, 30141, 105371로 D군이 가장 높았으며, A, B, C군과는 유의한 차이가 있었다(P<.05). 3. 파절양상은 B군과D군에서는 고정체와 나사 모두에서 수직 (longitudinal)파절과 수평 (transverse)파절이 동시에 일어나는 복합 (complex mode) 파절이 관찰 되었고, A와 C군에서는 고정체에서 수평 (transverse mode) 파절만이 관찰되었다. 4. 유한요소분석 결과 인장응력이 가장 높은 고정체 표면부에서 피로 균열이 시발되어 압축응력이 가장 높은 반대편 부위로 피로균열이 전파되었으며, 최대 유효 응력값은 C군이 가장 높았고, B군에서 가장 낮았다. 결론: 피질골 높이와 일치하는 임플란트 고정체 부위에서 최대 인장 주응력이 발생되며, 고정체 사공간부 (dead space)가 최대 인장 주응력이 작용하는 지그 표면과 일치할 때 피로파절이 발생되었다. 따라서 악골에 식립된 임플란트의 신뢰성을 향상시키고 수명을 증대시키기 위해서는 가능한 임플란트 주위의 골소실이 일어나지 않도록 해야 할 것이나 골흡수가 일어나 사공간부 수준까지 진행된다면 임플란트의 파절 빈도가 증가될 수 있으므로 이에 대한 대처가 필요할 것으로 사료된다.

• 대한소아치과학회지
• /
• 제48권3호
• /
• pp.344-351
• /
• 2021

이 연구의 목적은 타이타늄-질소 코팅된 금속관(TiNCs)의 표면 경도와 스테인리스 스틸 금속관(SSCs)의 표면 경도를 비교하고, TiNCs의 부식 저항성 및 물리적 자극에 대한 금색 코팅의 안정성을 평가하는 것이다. 표면 경도 시험을 위해 10개의 TiNCs와 10개의 SSCs를 사용하였다. 각 금속관 종류당 총 30번의 경도를 측정하여 평균값을 구하고 비교하였다. 부식 저항성 시험을 위해 직사각형 형태의 TiNC와 SSC의 원재료(금속관으로 가공되기 전 판상 형태)를 준비하였다. 각 금속관 종류 당 2회의 부식 시험을 시행하였다. 부식 용액에 용출된 금속 이온의 총 양을 유도결합 플라즈마 분광분석기로 측정하였다. 5개의 TiNCs로 반복적으로 가해지는 칫솔력에 대한 색조 안정성 시험을 시행하였다. TiNCs의 평균 경도는 SSCs의 평균 경도보다 유의미하게 높았다. TiNCs와 SSCs의 원재료로부터 용출된 금속 이온의 총 합은 ISO 22674(재료의 무결성에 관한 기준) 기준치를 넘지 않음을 확인했다. TiNCs의 금색 코팅은 반복적인 물리적 자극에 대하여 주어진 시간 동안 안정성을 가졌다.

• 한국표면공학회지
• /
• 제54권5호
• /
• pp.267-277
• /
• 2021

Nitriding layers developed during gaseous nitriding of AISI4115 steels for the application of steel bushing part were investigated. The compound layer thickness of about 10㎛, 0.3mm of case depth under the same conditions, and conventional nitriding, nitrocarburizing, and controlled nitriding were performed in three methods. In the controlled nitriding, K_N was controlled by measuring the hydrogen partial pressure. The nitrided samples were analyzed by micro Vickers hardness test, optical microscopy and scanning electron microscopy. The phases of compound layer were identified by X-ray diffraction and electron backscatter diffraction. The controlled nitriding specimen indicated the highest surface hardness of about 860 HV_0.1. The compound layer of the conventional nitriding and nitrocarburizing specimen was formed with about 46% porous layer and 𝜺 + 𝜸' phase, and about 13% porous layer and about 80% 𝜸' phase were formed on the controlled nitriding specimen. As a result of the Ball-on-disk wear test, the worn mass loss of ball performed on the surface of the controlled nitriding specimen was the largest. The controlled nitriding specimen had the highest surface hardness due to the lowest porous percentage of compound layer, which improved the wear resistance.

• 한국표면공학회지
• /
• 제29권6호
• /
• pp.634-639
• /
• 1996

In oder to improve the wear resistance as well as oxidation resistance at high temperature a AISI H13 steel was treated by a duplex process of calorizing followed by plasma nitriding. The surface properties of the duplex-treated AISI H13 steel was characterized and compared with those treated by single surface process of calorizing and plasma nitriding, in terms of microstruture, microhardness, wear resistance at $500^{\circ}C$, and the oxidation behaviours at $700^{\circ}C$, Duplex process on H13 steel had created duplex layer of approximately $190\mu\textrm{m}$ on the surface, and surface microhardness was measured to be above 1450Hv(0.1Kgf). There was considerable improvement of the high temperature wear resistance at $500^{\circ}C$ in the duplex-treated steel when both wear volume and weight change due to oxidation were considered. In addition the duplex-treated steel showed an improved high temperature oxidation resistance than the plasma nitrided steel at $700^{\circ}C$.

• 한국표면공학회지
• /
• 제53권6호
• /
• pp.280-284
• /
• 2020

Electron beam irradiation is widely used as a type of surface modification technology to advance surface properties. In this study, the effect of electron beam irradiation on properties, such as surface hardness, wear resistance, roughness, and critical load of Titanium Aluminium nitride (TiAlN) films was investigated. TiAlN films were deposited on the SKD-61 substrate by using cathode arc ion plating. After deposition, the films were bombarded with intense electron beam for 10 minutes. The surface hardness was increased up to 4520 HV at electron irradiation energy of 1500 eV. In addition, surface root mean square (RMS) roughness of the films irradiated at 1500 eV shows the lowest roughness of 484 nm in this study.

• 한국분말재료학회지
• /
• 제29권4호
• /
• pp.325-331
• /
• 2022

Beta-titanium alloys are used in many industries due to their increased elongation resulting from their BCC structure and low modulus of elasticity. However, there are many limitations to their use due to the high cost of beta-stabilizer elements. In this study, biocompatible Ti-Mo-Fe beta titanium alloys are designed by replacing costly beta-stabilizer elements (e.g., Nb, Zr, or Ta) with inexpensive Mo and Fe elements. Additionally, Ti-Mo-Fe alloys designed with different Fe contents are fabricated using powder metallurgy. Fe is a strong, biocompatible beta-stabilizer element and a low-cost alloying element. The mechanical properties of the Ti-Mo-Fe metastable beta titanium alloys are analyzed in relation to the microstructural changes. When the Fe content increases, the tensile strength and elongation decrease due to brittle fracture despite a decreasing pore fraction. It is confirmed that the hardness and tensile strength of Ti-5Mo-2Fe P/M improve to more than 360 Hv and 900 MPa, respectively.