• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.608-613
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• 2012

We investigated the property changes of MgO powders sintered at temperatures ranging from $700^{\circ}C$ to $1900^{\circ}C$ for 5minutes at a pressure of 2.7 GPa for a high-pressure high-temperature(HPHT) diamond synthesis process. The physical properties of the sintered MgO powders were characterized by optical microscopy, field emission scanning electron microscopy (FE-SEM), Vickers hardness tests, and by the apparent density, and X-ray diffractometry. An optical micro-analysis showed that white MgO powders became black after sintering due to carbon contamination from the graphite heat source. FE-SEM revealed the growth in the grain size of the MgO powders from $0.3{\mu}m$ to $50{\mu}m$ after sintering at $1700^{\circ}C$. The hardness and apparent density increased to $1800^{\circ}C$ while the samples were dedensified at $1900^{\circ}C$ due to the growth of isolated pores. According to the XRD analysis, no phase transformation occurred in the MgO powders. These results suggest that HPHT-sintered MgO powders can show an accelerated sintering process characterized by grain neck growth, pore connections, isolated pore growth and dedensification in 5 minutes, while these processes with the conventional sintering process take at least 5 hours.

• Restorative Dentistry and Endodontics
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• v.30 no.3
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• pp.178-183
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• 2005

This study was done to evaluate whether vital bleaching agents could influence on the translucency of the bovine enamel. The anterior bovine teeth that were extracted one day before and without any gross discoloration were obtained and then were preserved in physiologic saline. 6 mm cylindrical tooth specimens were fabricated with diamond puncher perpendicularly on labial surface of bovine tooth. After embedded in transparent acrylic resin with labial surface being exposed, they were cut to a thickness of 1.2 mm with low speed diamond saw (Isomat, Buehler Co., Lake Bluff, IL, USA). They were smoothly ground to 1 mm thickness of enamel with sandpaper. 24 specimens were randomly divided into 3 groups and control group respectively. Opalescence (10% carbamide peroxide, Ultradent, South Jordan, USA), Rembrandt (10% carbamide peroxide, DenMat, USA) and Opalescence F (15% carbamide peroxide with fluoride, Ultradent, USA) were applied on labial sides of the bovine enamel for 7 days (bleaching agents were reapplied every 24 hours) and the opposite surface was contacted to cotton that soaked in distilled water. The control group was soaked in distilled water. Three stimulus value X, Y and Z were evaluated with colorimeter (Color ' Color Differencerneter, Model TC-6FX, Tokyo Denshoku Co., Japan) on the labial surface of all specimen three times on white and black background plate before the bleaching agents were applied and on 3rd, 5th and 7th day after applied. The degree of translucency was normally assessed by measuring the inverse property, opacity (contrast ratio). 10% Opalescence, 15% Opalescence-F, and control group showed no significant variation in the translucency of bovine enamel, However Rembrandt decreased the translucency of it (p < 0.01).

• Journal of the Korea Fashion and Costume Design Association
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• v.4 no.2
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• pp.139-161
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• 2002

This study investigates the characteristics of Nordic sweaters works from a historical perspective. Specifically, this study deals with the following research topics: 1) development of Nordic sweaters, 2) the characteristics of Nordic sweaters industry according to the change of times, 3) the comparison of local knitting patterns, 4) the symbolic meaning of the designs in the Nordic sweaters and patterns. The results of the study are summarized as follows. 1. Knitted work developed mostly in Northern Europe, a cold area, and the barren, mountainous coastal areas where people frequently used woolen materials for clothes. It was also developed in Scandinavian regions which lead the fashion in modern days. Scandinavian knitting techniques have been diffused into the east coast of England and Northern Europe by Vikings. 2. Scandinavian countries are distinguished from other countries by their conservative but creative cultural tradition. Their knitting patterns are characterized by small geometric figures such as dots, triangles, squares, rhombuses, and crosses used often with stars and roses. Scandinavian knitting is also salient for its vertical stripes and simple motifs repeating at short intervals. 1) Norway ; Simple and geometric Norwegian patterns are classified into three groups of motifs: (a) the motifs of cross, diamond, X, and swastika (equation omitted). (b) the motifs of human figures, animals and birds, (c) floral motifs (especially eight-petal roses). Their use of color is also simple, and is limited to more than two colors. (2) Sweden ; Swedish patterns are colorful and geometric. They are characterized by features such as brocade, complex embroidery, and contrast of red and black colors. They also show Guernsey patterns. Initials and production years were knitted in sweaters which have different patterns in their trunks and sleeves. 3) Denmark ; The Danish pattern is the purl stitch knitted against the stockinette stitch. The technique is used to copy woven damask motifs. The patterns are seen most clearly when they are knit with smooth yarn. The Faeroe sweaters are the representative work of Danish knitting. Faeroe knitting, incorporates stranded pattern and is knit in the round, either with circular needles. 4) Finland ; Finnish patterns are similar to Norwegian patterns. Finnish knitted work show very colorful, variety and free-flowing geometric patterns. 5) Iceland ; Icelandic knitting shows original ribbon pattern. Lope sweater is the representative work. 3. The traditional knitting patterns not only carried symbolic meanings but also served as means of communication. First of all, patterns had incantatory meanings. Patterns were symbolic of one's social standing, too. The colors, motifs and their arrangements were very important features symbolizing one's social position or family line. People often communicated by certain pieces of knitted work or patterns. In short, the knitted work in the Nordic sweaters served the function of admiring the beauty of nature and symbolizing various meanings. The unique designs and colors of the knitted work reflected the characteristics of the culture those works belonged to. This study also turns our attention to the issue of how the traditional colors and designs of the knitted work can contribute to the development of modern designs, and by doing so, if makes us realize the importance of knitted works in modern society.