Ju-Han Kim

Size-controllable and low-cost fabrication of graphene quantum dots using thermal plasma jet.

We report a size-controllable and low-cost fabrication method of graphene quantum dots (GQDs) using a thermal plasma jet. A carbon atomic beam was generated by injecting a large amount (2.5 L/min) of ethylene gas continuously into Ar plasma. The beam was then flowed through a carbon tube (5-20 cm in length) attached to the anode and then dispersed into a chamber. Carbon materials including GQDs were made by a gas phase collision reaction. The production rate of carbon soot was 40 g/h for a 2.5 L/min injection rate. Almost all of the carbon soot dispersed in ethanol by sonication, while isolated GQDs were dispersed in ethanol by stirring with a stirring rod. The weight percent of GQDs in carbon soot, based on the amount extracted in ethanol, was about 10%. This means that the production rate of GQDs was about 4 g/h. The average size of GQDs, with a relatively narrow size distribution, was controlled by varying the length of the carbon tube attached. It was about 10, 14, and 19 nm when the length was 5, 10, and 20 cm, respectively. The electric structure based on the photoluminescence data of our GQDs had a singlet ground state and was in good agreement with that of carbyne. Our GQDs will disperse in organic solvents such as toluene, but not in water. The dispersion properties also support that our GQDs have carbyne-like edges. We proposed that the PL peaks observed can be attributed to electronic transitions between energy levels of the GQDs having carbyne-like edges.

Fabrication of graphene flakes composed of multi-layer graphene sheets using a thermal plasma jet system

We have developed a method to fabricate graphene flakes composed of high quality multi-layer graphene sheets using a thermal plasma jet system. A carbon atomic beam was generated by injecting ethanol into Ar plasma continuously; the beam then flowed through a carbon tube attached to the anode. Graphene was made by epitaxial growth where a carbon atomic beam, having the proper energy, collided with a graphite plate. The graphene fabricated was very pure and showed a relatively good crystalline structure. We have demonstrated that the number of layers of graphene sheets could be controlled by controlling the rate of ethanol injection. Our process is a continuous process with a relatively high yield (approximately 8%).

Gray matter deficits in young adults with narcolepsy

Objectivesu2002–u2002 The aim of this study was to investigate gray matter volume changes in narcolepsy.

Graphene quantum dots as a highly efficient solution-processed charge trapping medium for organic nano-floating gate memory.

A highly efficient solution-processible charge trapping medium is a prerequisite to developing high-performance organic nano-floating gate memory (NFGM) devices. Although several candidates for the charge trapping layer have been proposed for organic memory, a method for significantly increasing the density of stored charges in nanoscale layers remains a considerable challenge. Here, solution-processible graphene quantum dots (GQDs) were prepared by a modified thermal plasma jet method; the GQDs were mostly composed of carbon without any serious oxidation, which was confirmed by x-ray photoelectron spectroscopy. These GQDs have multiple energy levels because of their size distribution, and they can be effectively utilized as charge trapping media for organic NFGM applications. The NFGM device exhibited excellent reversible switching characteristics, with an on/off current ratio greater than 10(6), a stable retention time of 10(4) s and reliable cycling endurance over 100 cycles. In particular, we estimated that the GQDs layer trapped ∼7.2xa0×xa010(12) cm(-2) charges per unit area, which is a much higher density than those of other solution-processible nanomaterials, suggesting that the GQDs layer holds promise as a highly efficient nanoscale charge trapping material.

Characteristics of graphene quantum dots determined by edge structures: three kinds of dots fabricated using thermal plasma jet

When a graphene sheet is cut along zigzag lines, carbene edges having two unshared valence electrons at each edge carbon atom are obtained, while along the armchair lines, carbyne edges having carbon triple bonds are obtained. Carbene and carbyne edges have polar and nonpolar characters, respectively. 90 degree corners are obtained when armchair and zigzag lines are encountered, while 120 degree corners are obtained when the same type of lines are encountered. Therefore, hexagonal graphene quantum dots (GQDs) are obtained when the same type of cutting lines are encountered at all the corners, while rectangular GQDs are obtained when different types of cutting lines are encountered. We have fabricated three types of GQDs by a gas phase collision reaction using a thermal plasma jet. Zigzag GQDs having only carbene edges were dispersed in polar solvents and they had basic hexagonal shapes. Armchair GQDs having only carbyne edges were dispersed in nonpolar solvents and they also had basic hexagonal shapes. Hybrid GQDs having both carbyne and carbene edges in each dot were dispersed in both polar and nonpolar solvents and had rectangular shapes. The photoluminescence and photoluminescence excitation spectra of hybrid GQDs responded to the combination of the spectra of zigzag and armchair GQDs.

The susceptibility of magpies to a highly pathogenic avian influenza virus subtype H5N1

Korean wild magpies (Pica pica sericea) were intranasally inoculated with highly pathogenic avian influenza (A/Chicken/Korea/ES/03 virus) (H5N1), which was classified as clade 2.5. We estimated viral replication, death after infection, and histology and immunohistochemistry. This species was highly susceptible to severe infection; 100% of birds died within 5 to 8 d. The virus was detected from oropharyngeal (1 to 5 d postinfection) and cloacal (3 to 5 d postinfection) swabs from infected magpies. At necropsy, the prominent lesions were coalescing necrosis of the pancreas with enlargement of livers and spleens. Microscopically, pancreas, brain, heart, adrenal gland, and kidney were most consistently affected with necrotic and inflammatory changes, and viral antigen was frequently demonstrated in the parenchyma of these organs. As a result, Korean wild magpies were very susceptible to avian influenza (H5N1) virus.

Overexpression of HSP47 in esophageal squamous cell carcinoma: clinical implications and functional analysis

Several biomarkers of esophageal squamous cell carcinoma (ESCC) have been explored to improve the prognosis of this disease. One of these, the 47-kDa heat shock protein (HSP47), has been screened as a potential biomarker by genomic profiling and is known to be overexpressed in some malignant diseases. In this study, we explored the role and evaluated the prognostic value of HSP47 expression in ESCC. The function of this protein was analyzed by assaying proliferation, wound healing, and colony formation in an HSP47-knockdown ESCC line. The prognostic implication of HSP47 expression was analyzed by immunohistochemical staining in 157 surgical specimens. HSP47 expression level and other clinical variables were analyzed using multivariate Cox proportional hazards models. Silencing of the HSP47 gene in the ESCC cell line inhibited cell proliferation and colony formation. HSP47 was highly expressed in ESCC tissue samples, compared with normal esophageal tissues. The level of immunohistochemical staining of HSP47 and pathologic stage were significantly correlated with overall and recurrence-free survival, as shown by multivariate analysis (P = 0.014 and 0.044, respectively). We found that overexpression of HSP47 is associated with poor prognosis in patients with ESCC and that this is consistent with the function of HSP47 in terms of increased cell proliferation and colony formation. These results suggest that HSP47 is a potential prognostic biomarker for ESCC and merits further research for novel diagnostic and therapeutic applications.

MR findings of desmoplastic cerebral astrocytoma of infancy: A case report

Desmoplastic cerebral astrocytoma of infancy (DCAI) presents as a large supratentorial mass consisting of a central cystic component and an enhancing solid component associated with peripheral dural attachment. We report the unusual MR findings of a DCAI that differed from previously reported cases in terms of the presence of calcification, which is not considered a feature of this tumor, and the absence of an enhancing peripheral dural component.

Effect of maternally derived antibody on sequential infection with highly virulent bursal disease virus in newly hatched broilers

&NA; Maternally derived antibodies (MDAs) are important for protection against very virulent infectious bursal disease virus (vvIBDV). In this study, 5‐day‐old commercial broilers with non‐uniform MDA titers (with a coefficient of variation of 50%) were challenged with vvIBDV and given free contact with each other during a 2‐week period. The chicks were assigned to four MDA‐titer subgroups, GI‐1 (very low MDA), GI‐2 (low MDA), GI‐3 (medium MDA), and GI‐4 (high MDA). Transient symptoms of infection were observed in 35.7% of challenged birds. Body weight gain was significantly lower in GI‐2, GI‐3, and GI‐4 birds than in an unchallenged control group. Seroconversion was observed in GI‐1 birds and some GI‐2 birds. The frequency of virus shedding via the cloaca in vvIBDV‐challenged birds increased from 7.1% of GI birds at 5 days post inoculation (dpi) to 35.7% at 14 dpi. The timing of virus shedding was progressively later from GI‐1 to GI‐4. At 14 dpi, significant atrophy of the bursa of Fabricius (BF) was observed in GI birds compared with GII controls; atrophy was most severe in GI‐1 birds and least severe in GI‐4 birds. BF lesion scores decreased from GI‐1 to GI‐4. The proportion of birds with IBDV antigen in the BF at 14 dpi was higher in GI‐2 and GI‐3 than in GI‐1 and GI‐4, whereas the viral load in positive birds increased from GI‐1 to GI‐4. Our results indicate that high levels of MDAs would protect chicks from initial vvIBDV infection but that progressive decay of these MDAs would result in delayed infection by virus shedding in initially infected birds with low MDA titers, resulting in continuous circulation of the virus in a flock with non‐uniform MDA titers.