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We present recent observation results of Sgr A* at millimeter obtained with VLBI arrays in Korea and Japan.
7 mm monitoring of Sgr A* is part of our AGN large project. The results at 7 epochs during 2013-2014, including high resolution maps, flux density and two-dimensional size measurements are presented. The source shows no significant variation in flux and structure related to the G2 encounter in 2014. According to recent MHD simulations by kawashima et al., flux and magnetic field energy can be expected to increase several years after the encounter; We will keep our monitoring in order to test this prediction.
Astrometric observations of Sgr A* were performed in 2015 at 7 and 3.5 millimeter simultaneously. Source-frequency phase referencing was applied and a combined ”core-shift” of Sgr A* and a nearby calibrator was measured. Future observations and analysis are necessary to determine the core-shift in each source.
We show how estimates of parameters characterizing inflation-based theories of structure formation localized over the past year when large scale structure (LSS) information from galaxy and cluster surveys was combined with the rapidly developing cosmic microwave background (CMB) data, especially from the recent Boomerang and Maxima balloon experiments. All current CMB data plus a relatively weak prior probability on the Hubble constant, age and LSS points to little mean curvature (Ωtot = 1.08±0.06) and nearly scale invariant initial fluctuations (ns = 1.03±0.08), both predictions of (non-baroque) inflation theory. We emphasize the role that degeneracy among parameters in the Lpk = 212 ± 7 position of the (first acoustic) peak plays in defining the Ωtot range upon marginalization over other variables. Though the CDM density is in the expected range (Ωcdmh2 = 0.17 ± 0.02), the baryon density Ωbh2 = 0.030 ± 0.005 is somewhat above the independent 0.019 ± 0.002 nucleosynthesis estimates. CMB+LSS gives independent evidence for dark energy (ΩΛ = 0.66 ± 0.06) at the same level as from supernova (SN1) observations, with a phenomenological quintessence equation of state limited by SN1+CMB+LSS to wQ < −0.7 cf. the wQ=−1 cosmological constant case.
Alcohol consumption is a possible co-factor of high-risk human papillomavirus (HR-HPV) persistence, a major step in cervical carcinogenesis, but the association between alcohol and continuous HPV infection remains unclear. This prospective study identified the association between alcohol consumption and HR-HPV persistence. Overall, 9230 women who underwent screening during 2002–2011 at the National Cancer Center, Korea were analysed in multivariate logistic regression. Current drinkers [odds ratio (OR) 2·49, 95% confidence interval (CI) 1·32–4·71] and drinkers for ⩾5 years (OR 2·33, 95% CI 1·17–4·63) had a higher risk of 2-year HR-HPV persistence (HPV positivity for 3 consecutive years) than non-drinkers and drinkers for <5 years, respectively (vs. HPV negativity for 3 consecutive years). A high drinking frequency (⩾twice/week) and a high beer intake (⩾3 glasses/occasion) had higher risks of 1-year (OR 1·80, 95% CI 1·01–3·36) HPV positivity for 2 consecutive years) and 2-year HR-HPV persistence (OR 3·62, 95% CI 1·35–9·75) than non-drinkers. Of the HPV-positive subjects enrolled, drinking habit (OR 2·68, 95% CI 1·10–6·51) and high consumption of beer or soju (⩾2 glasses/occasion; OR 2·90, 95% CI 1·06–7·98) increased the risk of 2-year consecutive or alternate HR-HPV positivity (vs. consecutive HPV negativity). These findings suggest that alcohol consumption might increase the risk of cervical HR-HPV persistence in Korean women.
Enterotoxigenic Escherichia coli (ETEC) is now recognized as a common cause of foodborne outbreaks. This study aimed to describe the first ETEC O169 outbreak identified in Korea. In this outbreak, we identified 1642 cases from seven schools. Retrospective cohort studies were performed in two schools; and case-control studies were conducted in five schools. In two schools, radish kimchi was associated with illness; and in five other schools, radish or cabbage kimchi was found to have a higher risk among food items. Adjusted relative risk of kimchi was 5·87–7·21 in schools that underwent cohort studies; and adjusted odds ratio was 4·52–12·37 in schools that underwent case-control studies. ETEC O169 was isolated from 230 affected students, and was indistinguishable from the isolates detected from the kimchi product distributed by company X, a food company that produced and distributed kimchi to all seven schools. In this outbreak, we found that the risk of a kimchi-borne outbreak of ETEC O169 infection is present in Korea. We recommend continued monitoring regarding food safety in Korea, and strengthening surveillance regarding ETEC O169 infection through implementation of active laboratory surveillance to confirm its infection.
The clinical impact of antimicrobial resistance on the outcome of pneumococcal bacteraemia has remained unclear. This study aimed to evaluate risk factors for mortality and determine the impact of antimicrobial resistance on clinical outcomes. A total of 150 adult patients with pneumococcal bacteraemia were identified over a period of 11 years at Seoul National University Hospital. Of the 150 patients, 122 (81·3%) had penicillin-susceptible (Pen-S) strains and 28 (18·7%) penicillin-non-susceptible (Pen-NS) strains; 43 (28·7%) had erythromycin-susceptible (EM-S) strains and 107 (71·3%) erythromycin-non-susceptible (EM-NS) strains. On multivariate analysis, elevated APACHE II score [odds ratio (OR) 1·24, 95% confidence interval (CI) 1·14–1·34, P<0·001) and presence of solid organ tumour (OR 2·99, 95% CI 1·15–7·80, P=0·025) were independent risk factors for mortality. Neither erythromycin resistance nor penicillin resistance had a significant effect on clinical outcomes. However, for the 76 patients with pneumococcal pneumonia, the time required for defervescence was significantly longer in the EM-NS group than in the EM-S group (5·45±4·39 vs. 2·93±2·56, P=0·03 by log rank test). In conclusion, antimicrobial resistance does not have an effect on mortality in adult patients with pneumococcal bacteraemia.
A series of ZnO thin films with various deposition temperatures were prepared on (100) GaAs substrates by radio-frequency magnetron sputtering using ZnO target. The ZnO films were studied by field emission scanning electron microscope(FESEM), x-ray diffraction(XRD), photoluminescence(PL), cathodoluminescence(CL), and Hall measurements. The structural, optical, and electrical properties of the films were discussed as a function of the deposition temperature. With increasing temperature, the compressive stress in the films was released and their crystalline and optical properties were improved. From the depth profile of As measured by secondary ion mass spectrometry(SIMS), As doping was confirmed, and, in order to activate As dopant atoms, post-annealing treatment was performed. After annealing treatment, electrical and optical properties of the films were changed.
The relation between the ion irradiation induced grain growth in bilayer system and the basic parameters involved in ion beam mixing process was studied. TEM micrographs showed that a significant grain growth has been induced by Ar+ irradiation at room temperature. The grain size increases rapidly in low dose region, while it approaches a saturated value in high dose region, and it has close relationship with thermodynamic properties such as cohesive energy ( ΔHc ) and heat of mixing( ΔHm ). The experimental results are in good agreement with the model for the grain growth based on the thermal spike induced atomic migration.
Amorphous semiconductors play a major role in the field of electronic imaging. The function of an image sensor is to generate an electrical signal corresponding to the light distribution in the optical image. The photodiodes convert light into electrical signal. We investigated the linear image sensor driven by thin film transistor as an switching element, with each photodiode connected to the corresponding thin film transistor. The photo/dark conductivity of photodiode are compared in the case of amorphous silicon and microcrystalline. The influences in contact resistance between microcrystalline n+ layer and the source/drain metal electrode, electron mobility, threshold voltage, and on-off current ratio of thin film transistor with intrinsic microcrystalline silicon channel layer were also investigated.
The adsorption and thermal behavior of tetrakis-(dimethylamido)-titaniurn (TDMAT), Ti[NMe2]4, were investigated by surface spectroscopic techniques in the temperature range 100-1100K. A metallic Ti substrate readily dissociates TDMAT even below 300 K, producing a carbon-rich interface. When the substrate is exposed to a continuous flux of TDMAT at growth temperatures (550-700K), deposition of carbon-rich TiCxNy films readily occurs with a high precursor reactive sticking coefficient. With the addition of sufficient NH3 flux, we demonstrate the existence of a direct surface-reaction-driven deposition mechanism which involves reaction(s) between adsorbed TDMAT and NHX species on the film surface and thus leads to growth of substantially cleaner TiNx films. This growth mechanism dominates at low pressures (≤10-4Torr) where gas-phase reaction between the precursor gases becomes insignificant.
Effects of RF sputtering on the hydrothermal stability of Cr/polyimide interfaceshave been studied using FTIR, XPS, and peel test. It has been found that RF sputter-treatment of polyimnide surface prior to metal deposition leads to an enhancement of adhesion through chemical bonding of the metal with polyimide resulting in cohesive polyimide failure. The RF sputter treatment of polyimide, however, simultaneously modifies the polyimide underneath its surface. The adhesion strength of the Cr/polyimide interfaceis degraded significantly upon exposure to a temperature/humidity (T/H) environment. It is suggested this degradation results from the hydrolysis of polyimide. The hydrolysis is facilitated by the presence of modified unstable polyimide near the interface. This degradation of adhesion strength can be minimized by converting the unstablemodified polyimide to a more stable state by re-curing the Cr/polyimide interfacebefore exposure to T/H environment.
The asymmetric amorphous silicon thin film transistors are fabricated and exposed to various stress environments. A visible light illumination of 200,000 Ix and gate bias of 30 V are applied to both asymmetric and widely used symmetric a-Si TFT's. It is observed that the leakage current of asymmetric structure, where only one electrode is fully overlapped by gate electrode, is much less than that of symmetric one. The visible light illumination as well as gate bias stress do not degrade the leakage current of the asymmetric a-Si TFT's, while the leakage current in die symmetric TFT's are increased considerably due to the stress. Also, the degree of degradation in the threshold voltage, the field effect mobility and the subthreshold slope of asymmetric TFT's are relatively much less than that of conventional symmetric TFT's.
The accelerated degradation phenomena in amorphous silicon thin film transistors due to both electrical stress and visible light illumination under the elevated temperature have been investigated systematically as a function of gate bias, light intensity, and stress time. It has been found that, in case of electrical stress, the threshold voltage shifts of a-Si TFT's may be attributed to the defect creation process at the early stage, while the charge trapping phenomena may be dominant when the illumination periods exceed about 2 hours. It has been also observed that the degradation in the device characteristics of a-Si TFT's is accelerated due to multiple stress effects, where the defect creation mechanism may be more responsible for the degradation rather than the charge trapping mechanism.
In contrast to the bulk diluted magnetic semiconductor (DMS) Cd1−xMnxSe which occurs with the wurtzite structure, its epilayers grown on (001) GaAs substrate by Molecular Beam Epitaxy exhibit the cubic zinc-blende structure. Raman spectroscopy and photoluminescence studies on this novel DMS show (1) a “two-mode” behavior of the zone center optical phonons, (2) the Raman line associated with the spin-flip in the Zeeman split S = 5/2 ground state of Mn2+, and (3) large Raman shifts associated with the spin-flip of donor-bound electrons. The large magnetic field dependence in (3) with saturation at high fields and low temperature shows that the s-d exchange interaction characteristic of DMS's is also manifested strikingly in the zinc-blende phase of Cd1−xMnxSe.
In this work, we proposed a direct bonding method using interlayers for single crystalline silicon wafers and glass wafers. Various materials were used for interlayers of thermal oxide, sputtered nitride, electron-beam(E-beam) evaporated silicon oxide and molybdenum. After hydrophilization, samples were spin dried and mated together without external forces. Three types of solutions were used for hydrophilizing the samples. Changes of average surface roughness after hydrophilization of the single crystalline silicon wafer, thermal oxide and E-beam silicon-oxide were inspected using atomic force microscope(AFM). Bonding interfaces of the bonded pairs were observed by scanning electron microscope(SEM). Voids and non-contact areas of the bonding pairs were also inspected using infrared(IR) transmission microscope. Surface energy, tensile strength measurements and breaking tests were also done.
Liquid and volatile (hfac)CuL compounds where hfac = 1,1,1,5,5,5-hexafluoro- 2,4-pentanedionate and L = 1-pentene (1), acetyltrimethylsilane (2), and vinyltri- methoxysilane (3) were newly developed for reproducible copper deposition. During CVD processes, no premature decomposition of the precursor was observed in the source reservoir that contained the mixture of (hfac)CuL and excess free ligand L. Pure Cu films were deposited in the deposition temperature range 180°C ˜ 220°C
A silicon-to-silicon anodic bonding process using a glass layer deposited by electron beam evaporation will be described. Corning #7740 Pyrex glass was used the source material of electron evaporation. From Auger electron spectroscopy (AES), the composition of the deposited glass layer is nearly same as that of the bulk Pyrex glass plate. Wafers are bonded at a temperature as low as 135 °C with an applied voltage as small as 35Vdc, enabling of this technique to be applied to vacuum packaging of microelectronic devices. Experimental results reveal that an evaporated glass layer of more than 1 μ m thick is suitable for anodic bonding. Finally, The role of sodium ions in anodic bonding was also studied by investigating the theoretical bonding mechanism and examining the results of secondary ion mass spectroscopy (SIMS) analysis.
The barrier heights of various Schottky diodes in n-type 4H-SiC and 6H-SiC is estimated from published data at Si-face and C-face, respectively, employing the LSM (least square method). It is found that the barrier height in SiC Schottky diode is a linear function of metal work function as φB. =a φm + b. The a is about 0.63 ∼ 0.72. The already established analytic expression in  is compared with the estimated linear expression and revised by employing the empirical factor, α between the upper and lower boundary of interface state density, DIT. The values of a lie in 1.65 ∼ 32.1.