Showing papers by "Sungkyunkwan University published in 2004"

Ultra-large-scale syntheses of monodisperse nanocrystals.

Abstract: The development of nanocrystals has been intensively pursued, not only for their fundamental scientific interest, but also for many technological applications. The synthesis of monodisperse nanocrystals (size variation <5%) is of key importance, because the properties of these nanocrystals depend strongly on their dimensions. For example, the colour sharpness of semiconductor nanocrystal-based optical devices is strongly dependent on the uniformity of the nanocrystals, and monodisperse magnetic nanocrystals are critical for the next-generation multi-terabit magnetic storage media. For these monodisperse nanocrystals to be used, an economical mass-production method needs to be developed. Unfortunately, however, in most syntheses reported so far, only sub-gram quantities of monodisperse nanocrystals were produced. Uniform-sized nanocrystals of CdSe (refs 10,11) and Au (refs 12,13) have been produced using colloidal chemical synthetic procedures. In addition, monodisperse magnetic nanocrystals such as Fe (refs 14,15), Co (refs 16-18), gamma-Fe(2)O(3) (refs 19,20), and Fe(3)O(4) (refs 21,22) have been synthesized by using various synthetic methods. Here, we report on the ultra-large-scale synthesis of monodisperse nanocrystals using inexpensive and non-toxic metal salts as reactants. We were able to synthesize as much as 40 g of monodisperse nanocrystals in a single reaction, without a size-sorting process. Moreover, the particle size could be controlled simply by varying the experimental conditions. The current synthetic procedure is very general and nanocrystals of many transition metal oxides were successfully synthesized using a very similar procedure.

Evidence for an Oscillatory Signature in Atmospheric Neutrino Oscillations

Abstract: Muon neutrino disappearance probability as a function of neutrino flight length $L$ over neutrino energy $E$ was studied. A dip in the $L/E$ distribution was observed in the data, as predicted from the sinusoidal flavor transition probability of neutrino oscillation. The observed $L/E$ distribution constrained ${\ensuremath{ u}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{ u}}_{\ensuremath{\tau}}$ neutrino oscillation parameters; $1.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}l\ensuremath{\Delta}{m}^{2}l3.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }{\mathrm{e}\mathrm{V}}^{2}$ and ${sin }^{2}2\ensuremath{\theta}g0.90$ at 90% confidence level.

Market Stress and Herding

Abstract: We propose a new approach to detecting and measuring herding, which is based on the cross-sectional dispersion of the factor sensitivity of assets within a given market This method enables us to evaluate if there is herding towards particular sectors or styles in the market, including the market index itself, and critically we can also separate such herding from common movements in asset returns induced by movements in fundamentals We apply the approach to an analysis of herding in the US and South Korean stock markets and find that herding towards the market shows significant movements and persistence independently from and given market conditions and macro factors We find evidence of herding towards the market portfolio in both bull and bear markets Contrary to common belief, the Asian Crisis and, in particular, the Russian Crisis reduced herding and are clearly identified as turning points in herding behaviour

Observation of the narrow state X(3872) → J/ψπ+π- in p̄p collisions at √s = 1.96 TeV

Abstract: The observation of a state consistent with X(3872) decaying into J/ψπ+π- was reported. The X(3872) mass was measured to be 3871.3±0.7(stat)±0.4(syst)MeV/c2 from a sample of 730±90 candidates. The observed width was consistent with the detector resolution. The results were found to be converging well with the measurements by the Belle Collaboration using b± decays.

Search for dark matter WIMPs using upward through-going muons in Super-Kamiokande

Abstract: We present the results of indirect searches for Weakly Interacting Massive Particles (WIMPs), with 1679.6 live days of data from the Super-Kamiokande detector using neutrino-induced upward through-going muons. The search is performed by looking for an excess of high energy muon neutrinos from WIMP annihilations in the Sun, the core of the Earth, and the Galactic Center, as compared to the number expected from the atmospheric neutrino background. No statistically significant excess was seen. We calculate the flux limits in various angular cones around each of the above celestial objects. We obtain conservative model-independent upper limits on the WIMP-nucleon cross section as a function of WIMP mass, and compare these results with the corresponding results from direct dark matter detection experiments.

The tumour suppressor RASSF1A regulates mitosis by inhibiting the APC–Cdc20 complex

Abstract: The tumour suppressor gene RASSF1A is frequently silenced in lung cancer and other sporadic tumours as a result of hypermethylation of a CpG island in its promoter1,2,3,4,5,6. However, the precise mechanism by which RASSF1A functions in cell cycle regulation and tumour suppression has remained unknown. Here we show that RASSF1A regulates the stability of mitotic cyclins and the timing of mitotic progression. RASSF1A localizes to microtubules during interphase and to centrosomes and the spindle during mitosis. The overexpression of RASSF1A induced stabilization of mitotic cyclins and mitotic arrest at prometaphase. RASSF1A interacts with Cdc20, an activator of the anaphase-promoting complex (APC), resulting in the inhibition of APC activity. Although RASSF1A does not contribute to either the Mad2-dependent spindle assembly checkpoint or the function of Emi1 (ref. 1), depletion of RASSF1A by RNA interference accelerated the mitotic cyclin degradation and mitotic progression as a result of premature APC activation. It also caused a cell division defect characterized by centrosome abnormalities and multipolar spindles. These findings implicate RASSF1A in the regulation of both APC–Cdc20 activity and mitotic progression.

Chitosan sponges as tissue engineering scaffolds for bone formation

Abstract: Rat calvarial osteoblasts were grown in porous chitosan sponges fabricated by freeze drying. The prepared chitosan sponges had a porous structure with a 100–200 μm pore diameter, which allowed cell proliferation. Cell density, alkaline phosphatase activity and calcium deposition were monitored for up to 56 d culture. Cell numbers were 4 × 106 (day 1), 11 × 106 (day 28) and 12 × 106 (day 56) per g sponge. Calcium depositions were 9 (day 1), 40 (day 28) and 48 (day 56) μg per sponge. Histological results corroborated that bone formation within the sponges had occurred. These results show that chitosan sponges can be used as effective scaffolding materials for tissue engineered bone formation in vitro.

Estimated exposure to phthalates in cosmetics and risk assessment

Abstract: Some phthalates such as di(2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate (DBP) and their metabolites are suspected of producing teratogenic or endocrine-disrupting effects. To predict possible human exposure to phthalates in cosmetics, the levels of DEHP, diethyl phthalate (DEP), DBP, and butylbenzyl phthalate (BBP) were determined by high-performance liquid chromatography (HPLC) in 102 branded hair sprays, perfumes, deodorants, and nail polishes. DBP was detected in 19 of the 21 nail polishes and in 11 of the 42 perfumes, and DEP was detected in 24 of the 42 perfumes and 2 of the 8 deodorants. Median exposure levels to phthalates in cosmetics by dermal absorption were estimated to be 0.0006 g/kg body weight (bw)/d for DEHP, 0.6 g/kg bw/d for DEP, and 0.103 g/kg bw/d for DBP. Furthermore, if phthalates in cosmetics were assumed to be absorbed exclusively via 100% inhalation, the median daily exposure levels to phthalates in cosmetics were estimated to be 0.026 g/kg bw/d for DEHP, 81.471 g/kg bw/d for DEP, and 22.917 g/kg bw/d for DBP, which are far lower than the regulation levels set buy the Scientific Committee on Toxicity, Ecotoxicity, and the Environment (CSTEE) (37 g/kg bw/d, DEHP), Agency for Toxic Substances and Disease Registry (ATSDR) (7000 g/kg bw/d, DEP), and International Programme on Chemical Safety (IPCS) (66 g/kg bw/d, DBP), respectively. Based on these data, hazard indices (HI, daily exposure level/regulation level) were calculated to be 0.0007 for DEHP, 0.012 for DEP, and 0.347 for DBP. These data suggest that estimated exposure to-phthalates in the cosmetics mentioned are relatively small. However, total exposure levels from several sources may be greater and require further investigation.

Toxicological Characteristics of Endocrine-Disrupting Chemicals: Developmental Toxicity, Carcinogenicity, and Mutagenicity

Abstract: It is generally accepted that endocrine-disrupting chemicals (EDCs) play a role in a variety of adverse health effects in an intact organism or its progeny as a consequence of changes in the endocrine system. Primary toxic effects of EDCs were reported to be related to infertility, reduction in sperm count, and teratogenicity, but other important toxic effects of EDCs such as carcinogenicity and mutagenicity have also been demonstrated. The aim of the present study was to systematically analyze the toxicological characteristics of EDCs in pesticides, industrial chemicals, and metals. A comprehensive literature survey on the 48 EDCs classified by the Centers for Disease Control and Prevention (CDC) was conducted using a number of databases which included Medline, Toxline, and Toxnet. The survey results revealed that toxicological characteristics of EDCs were shown to produce developmental toxicity (81%), carcinogenicity (79%, when positive in at least one animal species; 48%, when classified based on IARC evaluation), mutagenicity (79%), immunotoxicity (52%), and neurotoxicity (50%). Regarding the hormone-modulating effects of the 48 EDCs, estrogenic effects were the most predominant in pesticides, while effects on thyroid hormone were found for heavy metals. EDCs showing estrogen-modulating effects were closely related to carcinogenicity or mutagenicity with a high degree of sensitivity. Systematic information on the toxicological characteristics of the EDCs will be useful for future research directions on EDCs, the development of new screening methods, legal regulation, and for investigations of their mechanism of action.

Inhibition of HIV-1 reverse transcriptase and protease by phlorotannins from the brown alga Ecklonia cava.

Abstract: The bioassay-directed isolation of a marine brown alga, Ecklonia cava, afforded four phlorotannin derivatives, eckol (1), 8,8′-bieckol (2), 8,4′′′-dieckol (3), and phlorofucofuroeckol A (4). Among these compounds, 2 and 3 exhibited an inhibitory effect on human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) and protease. Specifically, they inhibited the RT more potently than the protease. The inhibitory activity of compound 2 (IC50, 0.51 μM) against HIV-1 RT was comparable to that of nevirapine (IC50, 0.28 μM), a reference compound. An enzyme kinetic assay showed that this compound inhibited the RNA-dependent DNA synthesis activity of HIV-1 RT noncompetitively against dUTP/dTTP with a Ki value of 0.78 μM. With respect to the homopolymeric template/primer, (rA)n(dT)15, 8,8′-bieckol (2) displayed an uncompetitive type of inhibition (Ki, 0.23 μM).

Inclusive measurement of the photon energy spectrum in b → sγ decays

Abstract: We report a fully inclusive measurement of the flavor changing neutral current decay $b\ensuremath{\rightarrow}s\ensuremath{\gamma}$ in the energy range $1.8\text{ }\mathrm{G}\mathrm{e}\mathrm{V}\ensuremath{\le}{E}_{\ensuremath{\gamma}}^{*}\ensuremath{\le}2.8\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$, covering 95% of the total spectrum. Using $140\text{ }\mathrm{f}{\mathrm{b}}^{\mathrm{\ensuremath{-}}\mathrm{1}}$, we obtain $\mathcal{B}(b\ensuremath{\rightarrow}s\ensuremath{\gamma})=(3.55\ifmmode\pm\else\textpm\fi{}{0.32}_{\ensuremath{-}0.31\ensuremath{-}0.07}^{+0.30+0.11})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, where the errors are statistical, systematic, and from theory corrections. We also measure the first and second moments of the photon energy spectrum above $1.8\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$ and obtain $\ensuremath{\langle}{E}_{\ensuremath{\gamma}}\ensuremath{\rangle}=2.292\ifmmode\pm\else\textpm\fi{}0.026\ifmmode\pm\else\textpm\fi{}0.034\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$ and $\ensuremath{\langle}{E}_{\ensuremath{\gamma}}^{2}\ensuremath{\rangle}\ensuremath{-}\ensuremath{\langle}{E}_{\ensuremath{\gamma}}{\ensuremath{\rangle}}^{2}=0.0305\ifmmode\pm\else\textpm\fi{}0.0074\ifmmode\pm\else\textpm\fi{}0.0063\text{ }{\mathrm{G}\mathrm{e}\mathrm{V}}^{2}$, where the errors are statistical and systematic.

Study of B-→D**0π-(D**0→D(*)+π-) decays

Abstract: We report the results of a study of charged B decays to the D(+/-)pi(-/+)pi(-/+) and D(*+/-)pi(-/+)pi(-/+) final states using complete D-(*) reconstruction. The contributions of two-body B-->D**pi decays with narrow (j=3/2) and broad (j=1/2) D** states have been determined and the masses and widths of four D** states have been measured. This is the first observation of the broad P-wave D-0*(0) and D'(0)(1) mesons. The analysis is based on a data sample of 65 million B(B) over bar pairs collected in the Belle experiment.

Insulin resistance and C-reactive protein as independent risk factors for non-alcoholic fatty liver disease in non-obese Asian men.

Abstract: Background and Aim: Although insulin resistance is often considered the link between obesity and non-alcoholic fatty liver disease (NAFLD), the role of insulin resistance, independent of obesity, as a NAFLD risk factor in non-obese men has been less well established. Systemic inflammation may be accompanied by insulin resistance in healthy subjects. The goal of the present study was to examine if insulin resistance and systemic inflammatory markers are independent predictors of NAFLD in non-obese men. Methods: The authors conducted a cross-sectional survey of 120 patients with NAFLD and 240 controls matched by age and body mass index. Controls had no evidence of alcohol abuse, hepatitis B or C, obesity, or previous history of diabetes, fasting hyperglycemia or hypertension. Diagnosis of NAFLD was based on an elevated alanine aminotransferase level and sonographic evidence of a fatty liver. Insulin resistance was determined using a homeostasis model assessment (HOMA-IR). Results: The age-adjusted risk of developing NAFLD was strongly associated with the elevated levels in measurements of uric acid, fasting blood sugar, triglycerides, apolipoprotein B, C-reactive protein (CRP) and HOMA-IR, and decreased levels of high density lipoprotein cholesterol and apolipoprotein A-I. Multivariate analysis based on univariate analysis indicated that an increase in CRP (odds ratio [OR] = 1.37; 95% confidence interval [CI]: 1.06–1.77) per 1 SD (1.48 mg/L) and HOMA-IR (OR = 2.28; 95% CI: 1.67–3.11) per 1 SD (0.63) were independent risk factors for NAFLD. Conclusion: Insulin resistance and systemic inflammatory response are of key importance for inducing NAFLD, particularly in apparently healthy non-obese men.

Distribution of vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide receptors (VPAC1, VPAC2, and PAC1 receptor) in the rat brain.

Abstract: To examine the distributions of VIP/PACAP receptors (VPAC1, VPAC2, and PAC1 receptors) in the brain and to identify the cell types that express these receptors, we performed immunohistochemistry and double immunofluorescence in the rat brain with specific antibodies. The immunohistochemistry revealed that the receptors had distinctive, complementary, and overlapping distribution patterns. High levels of the VPAC1 receptor were expressed in the cerebral cortex, hippocampal formation, deep cerebellar nuclei, thalamus, hypothalamus, and brainstem. The VPAC2 receptors were concentrated in the cerebral cortex, hippocampal formation, amygdalar regions, cerebellar cortex, deep cerebellar nuclei, hypothalamus, and brainstem. On the other hand, the PAC1 receptors had a more restricted distribution pattern in the brain, and high levels of the PAC1 receptors were confined to the cerebellar cortex, deep cerebellar nuclei, epithalamus, hypothalamus, brainstem, and white matter of many brain regions. Also, many fibers expressing the PAC1 receptors were observed in various areas, i.e., the thalamus, hypothalamus, and brainstem. The double immunofluorescence showed that the VIP/PACAP receptors were confined to the neuroglia as well as the neurons. All three types of the VIP/PACAP receptors were expressed in the astrocytes, and the PAC1 receptors were also expressed in the oligodendrocytes. These findings indicate that VIP and PACAP exert their functions through their receptors in specific locations in different combinations. We hope that this first demonstration of the distributions of the VIP/PACAP receptors provides data useful in the investigation of the mechanisms of the many functions of VIP and PACAP in the brain, which require further elucidation. J. Comp. Neurol. 476:388–413, 2004. © 2004 Wiley-Liss, Inc.

Mach-Zehnder interferometer formed in a photonic crystal fiber based on a pair of long-period fiber gratings.

Abstract: We demonstrate implementation of an all-fiber Mach–Zehnder interferometer formed in a photonic crystal fiber (PCF). We formed the all-PCF Mach–Zehnder interferometer by mechanically inducing two identical long-period fiber gratings (LPGs) in the PCF. The spectral properties of a LPG and a LPG pair were investigated. The interference fringe formed within the stop band of the LPG pair varied with the period and the strength of the gratings, and the fringe spacing was decreased with increasing grating separation. From the fringe spacing measurement the differential effective group index of the PCF was calculated to be Δm≈2.8×10-3.

Magnetism in all-carbon nanostructures with negative Gaussian curvature

Abstract: We apply the ab initio spin density functional theory to study magnetism in all-carbon nanostructures. We find that particular systems, which are related to schwarzite and contain no undercoordinated carbon atoms, carry a net magnetic moment in the ground state. We postulate that, in this and other nonalternant aromatic systems with negative Gaussian curvature, unpaired spins can be introduced by sterically protected carbon radicals.

Precise measurement of the solar neutrino day-night and seasonal variation in Super-Kamiokande-I

Abstract: The time variation of the elastic scattering rate of solar neutrinos with electrons in Super-Kamiokande-I was fit to the variations expected from active two-neutrino oscillations. The best fit in the large mixing angle solution has a mixing angle of ${\mathrm{tan}}^{2}\ensuremath{\theta}=0.55$ and a mass squared difference of $\ensuremath{\Delta}{m}^{2}=6.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}{\mathrm{eV}}^{2}$ between the two neutrino mass eigenstates. The fitted day-night asymmetry of $\ensuremath{-}1.8\ifmmode\pm\else\textpm\fi{}1.6(\mathrm{stat}{)}_{\ensuremath{-}1.2}^{+1.3}(\mathrm{syst})%$ has improved statistical precision over previous measurements and agrees well with the expected asymmetry of $\ensuremath{-}2.1%.$

Benzene-templated hydrothermal synthesis of metal-organic frameworks with selective sorption properties.

Abstract: In this paper, we report two metal-organic frameworks [Co 3 (ndc) 3 -(bipyen) 1 5 ].H 2 O (1) and [Co 2 (ndc) 2 (bipyen)].C 6 H 6 .H 2 O (2) (bipyen = trans-1,2-bis(4-pyridyl)ethylene, H 2 ndc=2,6-naphthalenedicarboxylic acid). These compounds were both synthesized from identical hydrothermal reaction conditions except that benzene was added to the reaction for 2. Crystal structures show that the two compounds have triply interpenetrated three-dimensional frameworks and these frameworks have the same primary structure of a two-dimensional network of interconnected [Co 2 -(O 2 CR) 4 / 2 ] (R=naphthalene group) paddle-wheels and bridging bipyen ligands. Both compounds have guest water molecules and, in addition, 2 has guest benzene molecules. Structural transformations of the host accompanied guest removal, which can be monitored by powder X-ray diffraction. N 2 adsorption data of 2 show that there are two different types of pores corresponding to the benzene and water pores. Upon exposure to vapors of several organic molecules, the heat-treated sample of 2 adsorbs benzene and cyclohexene, but does not adsorb toluene, (o-, m-, and p-)xylenes, cycloheptatriene, or cyclohexane.