• Journal of Korean Society of Forest Science
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• v.94 no.2 s.159
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• pp.67-72
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• 2005

The objectives of this study were to identify the period of initiation of floral primordia in black locust (Robinia pseudoacacia L.) and subsequent development of floral buds until following spring. Four mature trees of black locust located in Suwon, Korea were selected. Bud samples were collected from the current-year shoots, starting from mid June to July every week, from August to October and from February to April every month. The buds were fixed in FAA solution, dehydrated, and imbedded in paraffin for microscopic observation. Buds collected on June 16, and 23, 1997, contained primitive primordia that might be interpreted as early floral primordia. By June 30, a bud showed a positive indication of inflorescence primordium with a well-formed shoot apex. All the inflorescence primordia observed throughout the collection periods were always associated with unique hairy appendages around the primordium and enclosed within a sclerenchymatous chamber. By July 7 and 15, a floral apex had early bud scales. By July 22, primitive inflorescence developed into visible arrangement of individual floral primordial By July 29, the inflorescence developed into whirl arrangement of individual floral primordia in a transverse section, but showed little further development until October 15. The inflorescence primordia seemed to over-winter at this stage. Buds collected from February 15 and March 24 the following year also showed no further development of inflorescence primordia. By April 7 the inflorescence started to show further development with elongated axis. At this time individual flowers were easily recognized.

• Composites Research
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• v.12 no.6
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• pp.8-14
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• 1999

This research is focused on the investigation of impact strength and the microscopic observation of material behavior of glass fiber reinforced polypropylene in solid phase forming. The fiber weight per-centage of the composite materials was 20%, 30% and 40%. The solid-phase formed specimens were pre-strained to 10%,20%. and 30% strain levels. The forming temperatures of specimens were $100^{\circ}C$, $125^{\circ}C$ and $150^{\circ}C$. Izod impact test was performed with unnotched specimens. With increasing the glass fiber content ; the impact strength was increased.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.3
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• pp.455-463
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• 2003

The aim of this study is to investigate the hydrogen embrittlement of Zr-2.5Nb CANDU pressure tube at room temperature. The transverse tensile and fracture toughness tests were performed at various hydrogen concentrations using transverse tensile specimens and CCT (curved compact tension) specimens. These specimens were directly machined from the pressure tube retaining original curvatures. Based on the results of these tests. the hydrogen embrittlement phenomenon was clearly observed and fracture toughness parameters of Zr-2.5Nb pressure tube materials such as, $K_{J(0.2)}$.$J_{ML}$.dJ/da, were dramatically decreased with the increasement of the hydrogen concentration. From microscopic observation by SEM and TEM, it was also revealed that various shapes dimples, fissures and quasi-cleavage were found at the hydrogen-absorbed materials with hydrides while traditional shape dimples were generally located at the as-received materials Through the comparison of the hydride and fissure lengths with the hydrogen concentration the new evaluation method of hydrogen embrittlement was suggested.

• Geomechanics and Engineering
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• v.12 no.6
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• pp.919-933
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• 2017

A series of Brazilian tests under diameter compression for disc specimens was carried out to investigate the strength and failure behavior by using acoustic emission (AE) and photography monitoring technique. On the basis of experimental results, load-displacement curves, AE counts, real-time crack evolution process, failure modes and strength property of granite specimens containing two pre-existing holes were analyzed in detail. Two typical types of load-displacement curves are identified, i.e., sudden instability (type I) and progressive failure (type II). In accordance with the two types of load-displacement curves, the AE events also have different responses. The present experiments on disc specimens containing two pre-existing holes under Brazilian test reveal four distinct failure modes, including diametrical splitting failure mode (mode I), one crack coalescence failure mode (mode II), two crack coalescences failure mode (mode III) and no crack coalescence failure mode (mode IV). Compared with intact granite specimen, the disc specimen containing two holes fails with lower strength, which is closely related to the bridge angle. The failure strength of pre-holed specimen first decreases and then increases with the bridge angle. Finally, a preliminary interpretation was proposed to explain the strength evolution law of granite specimen containing two holes based on the microscopic observation of fracture plane.

• Asian-Australasian Journal of Animal Sciences
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• v.8 no.6
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• pp.557-562
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• 1995

In this study, characteristics of chick primordial germ cells (PGCs), which is the founder cell of the germline, and gonadal development of the chick embryo between 12hrs and 6 day of incubation were investigated by transverse serial sections of chick embryos under the light microscopic observation. In embryo stage 20 (3 day of incubation), there are a lot of PGCs at the mesenchym, which were moving to the thickened epithelium (gonadal ridge). The PGCs arrive at both right and left gonad primordial in equal number prior to stage 24 (4 day of incubation), but in the following stages, the distribution of the PGCs became asymmetrical. More PGCs colonized the left than the right gonad, but the reason for the unequal distribution of PGCs is uncertain. The PGCs have mostly settled in the gonadal ridge (GR) at 6 day embryo. This study was conducted to investigate characteristics of the PGC migration and gonadal formation and observe the best condition for PGC isolation, culture and to attempt the possibility of the production for transgenic germline chimeras with manipulated PGCs.

• Applied Microscopy
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• v.31 no.3
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• pp.235-244
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• 2001

The aim of this study was to observe morphological changes of Trichomonas vaginalis after contact with human vaginal epithelial cells, by scanning electron microscope. The vaginal epithelial cells (VEC) (menstrual, days $5\sim10$) from normal women were mixed with T. vaginalis (VEC/trichomonads ratio of 1 : 10), and incubated for 30 min. The parasitic body was changed to a more elongated shape with pseudopodia or was flattened to ameboid transformation showing highly adherence to VEC.

• Korean Journal of Pharmacognosy
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• v.21 no.3
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• pp.210-216
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• 1990

Effects of the protein fraction of Panax ginseng on chicken embryonic skeletal muscle cells cultured with a decfiient medium were studied. The protein fraction was further fractionated into four groups according to the molecular weight; larger than 10,000 dalton(fraction A), between 5,000 and 10,000 dalton(fraction B), between 1,000 and 5,000 dalton(fraction C), between 500 and 1,000 dalton(fraction D). According to the microscopic observation, all four protein fractions at the concentration of $10{\sim}100{\;}{\mu}g/ml$ showed the tendency to stimulate the growth and differentiation of the muscle cells. The activity of acetylcholinesterase in muscle cells was significantly elevated by the protein fraction A at the concentration of $100{\mu}{\;}g/ml$. Protein fractions B,C and D significantly enhanced the synthesis of RNA in the muscle cells. The synthesis of DNA in muscle cells was significantly enhanced by protein fractions A,B and C.

• The Plant Pathology Journal
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• v.23 no.3
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• pp.151-154
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• 2007

Phytoplasma was identified from leaf lettuce (Lactuca sativa) cultivated in commercial green-house in Korea. Diseased leaf lettuce revealed proliferation of shoots, and yellowing and shrinking of leaves (lettuce proliferation-K). Polymerase chain reaction (PCR) with universal primer pair P1/P6, and aster yellows (AY) specific primer pair R16F1/R1 amplified 1.5kb and 1.1kb length of DNA fragments, respectively. Nucleotide sequences of 16S rRNA gene were determined (Gen Bank accession no EF489024). Phylogenetic analysis of 16S rDNA showed the closest relationship with AY phytoplasma (GenBank accession no. AY389822 and AY389826), indicating that lettuce proliferation-K is a member of AY. Phytoplasma bodies were detected in phloem sieve tubes of diseased lettuce by transmission electron microscopy. The structures had round or pleomorphic shapes with a diameter of 130-300nm. Phylogenetic analysis of 16S rRNA gene, microscopic observation of phytoplasma bodies and symptomatology indicated that lettuce proliferation-K is caused by phytoplasma in the AY group. This is the first report of phytoplasma disease in lettuce in Korea.

• The Plant Pathology Journal
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• v.24 no.3
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• pp.279-282
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• 2008

This study describes a phytoplasmal disease occurring in Petunia leaves grown in the glasshouse of the National Horticultural Research Institute, Suwon, Korea. Abnormal growth like flattened stem with flower malformation or phyllody was observed from the plant. The DNA extracted from the diseased leaves was amplified using a universal primer pair of P1/P6 derived from the conserved 16S rRNA gene of Mollicutes giving the expected polymerase chain reaction(PCR) product of 1.5 kb. In the nested PCR assays, the expected DNA fragment of 1.1 kb was amplified with the specific primer pair R16F1/R16R1 that was designed on the basis of aster yellows(AY) phytoplasma 16S rDNA sequences. The 1.1 kb PCR products were cloned and nucleotide sequences were determined, and the sequences of the cloned 168 rRNA gene were deposited in the GenBank database under the accession no. of EU267779. Analysis of the homology percent of the 168 rDNA of PFS-K showed the closest relationship with Hydrangea phyllody phytoplasma(AY265215), Brassica napus phytoplasma(EU123466) and AY phytoplasma CHRY(AY180956). Phytoplasma isolated from the diseased Petunia was designated as Petunia flat stem phytoplasma Korean isolate(PFS-K) in this study. Flattened stem occurring in Petunia was confirmed as infection of AY group of phytoplasma by determination of 16S rRNA gene sequences of phytoplasma and microscopic observation of phytoplasma bodies. This is the first report on the phytoplasmal disease in Petunia in Korea.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.5
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• pp.242-245
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• 2009

AlN crystals were grown by a sublimation process without seed crystals and the growth morphology of them was characterized. The grown AlN crystals were a polycrystalline phase, which had a diameter of $60\sim200\;{\mu}m$ and were grown with a growth rate of $0.2\sim0.5\;{\mu}n/hr$. It was observed that the as-grown crystals had a hexagonal crystal structure and revealed that these crystals were grown with a morphology of columnar morphology in the initial stage of the growth before they were enlarged in a way of a lateral growth behavior in the final stage. On the surface, a lot of pinholes were observed on the surface of crystals grown. The evolution of a growth morphology was characterized by optical and scanning electron microscopic observation.