Y. S. Hwang

Electron density and temperature measurement method by using emission spectroscopy in atmospheric pressure nonequilibrium nitrogen plasmas

A novel spectroscopic method is proposed for the measurement of electron density and temperature in atmospheric pressure dielectric barrier discharges using nitrogen gas. Simplified collisional-radiative models for the electronic and the vibrational states yield two separate continuity equations as a function of the electron density and the temperature with the coefficients expressed in terms of rotational temperature, vibrational temperature, and emission intensity ratio between the first positive system and the second positive system of nitrogen molecules. The electron density and the temperature in nonequilibrium atmospheric pressure plasmas can be determined by solving the continuity equations with the coefficients estimated from the spectroscopic measurements. It was confirmed by applying to a high power dielectric barrier discharge, where the measured plasma parameters were in good agreement with the estimation by using the electron conductivity of the discharge.

Medication Adherence and the Risk of Cardiovascular Mortality and Hospitalization Among Patients With Newly Prescribed Antihypertensive Medications

The importance of adherence to antihypertensive treatments for the prevention of cardiovascular disease has not been well elucidated. This study evaluated the effect of antihypertensive medication adherence on specific cardiovascular disease mortality (ischemic heart disease [IHD], cerebral hemorrhage, and cerebral infarction). Our study used data from a 3% sample cohort that was randomly extracted from enrollees of Korean National Health Insurance. Study subjects were aged ≥20 years, were diagnosed with hypertension, and started newly prescribed antihypertensive medication in 2003 to 2004. Adherence to antihypertensive medication was estimated as the cumulative medication adherence. Subjects were divided into good (cumulative medication adherence, ≥80%), intermediate (cumulative medication adherence, 50%–80%), and poor (cumulative medication adherence, <50%) adherence groups. We used time-dependent Cox proportional hazards models to evaluate the association between medication adherence and health outcomes. Among 33 728 eligible subjects, 670 (1.99%) died of coronary heart disease or stroke during follow-up. Patients with poor medication adherence had worse mortality from IHD (hazard ratio, 1.64; 95% confidence interval, 1.16–2.31; P for trend=0.005), cerebral hemorrhage (hazard ratio, 2.19; 95% confidence interval, 1.28–3.77; P for trend=0.004), and cerebral infarction (hazard ratio, 1.92; 95% confidence interval, 1.25–2.96; P for trend=0.003) than those with good adherence. The estimated hazard ratios of hospitalization for cardiovascular disease were consistent with the mortality end point. Poor medication adherence was associated with higher mortality and a greater risk of hospitalization for specific cardiovascular diseases, emphasizing the importance of a monitoring system and strategies to improve medication adherence in clinical practice.

Diabetes Mellitus and Risk of Thyroid Cancer: A Meta-Analysis

Introduction Diabetes mellitus (DM) is an important risk factor for endocrine cancers; however, the association with thyroid cancer is not clear. We performed a systematic review and meta-analysis to clarify the association between thyroid cancer and DM. Methods We searched MEDLINE, PUBMED and EMBASE databases through July 2012, using search terms related to diabetes mellitus, cancer, and thyroid cancer. We conducted a meta-analysis of the risk of incidence of thyroid cancer from pre-existing diabetes. Of 2,123 titles initially identified, sixteen articles met our inclusion criteria. An additional article was identified from a bibliography. Totally, 14 cohort and 3 case-control studies were selected for the meta-analysis. The risks were estimated using random-effects model and sensitivity test for the studies which reported risk estimates and used different definition of DM. Results Compared with individuals without DM, the patients with DM were at 1.34-fold higher risk for thyroid cancer (95% CI 1.11–1.63). However, there was heterogeneity in the results (p<0.0001). Sensitivity tests and studies judged to be high quality did not show heterogeneity and DM was associated with higher risk for thyroid cancer in these sub-analyses (both of RRs = 1.18, 95% CIs 1.08–1.28). DM was associated with a 1.38-fold increased risk of thyroid cancer in women (95% CI 1.13–1.67) after sensitivity test. Risk of thyroid cancer in men did not remain significant (RR 1.11, 95% CI 0.80–1.53). Conclusions Compared with their non-diabetic counterparts, women with pre-existing DM have an increased risk of thyroid cancer.

Impact of alcohol drinking on gastric cancer development according to Helicobacter pylori infection status

Background:Helicobacter pylori are major carcinogen of gastric cancer, but the associations among gastric cancer, H. pylori infection status, and alcohol consumption are not fully described. This study aimed to clarify how H. pylori infection status affects the association between alcohol consumption and gastric cancer risk.Methods:We selected 949 case–cohort participants from the 18 863 Korean Multi-center Cancer Cohort (KMCC) populations. Gastric cancer incidence inside and outside of the subcohort were 12 and 254 cases, respectively. Seropositivities for CagA, VacA, and H. pylori infection were determined by performing immunoblot assays. Weighted Cox regression models were used to calculate hazard ratios and 95% confidence intervals (CIs).Results:Relative to non-drinking, heavy drinking (⩾7 times a week), and binge drinking (⩾55 g alcohol intake per occasion) showed a 3.48-fold (95% CI, 1.13–10.73) and 3.27-fold (95% CI, 1.01–10.56) higher risk in subjects not previously infected by H. pylori. There was no significant association between drinking pattern and gastric cancer risk in H. pylori IgG seropositive subjects. An increased risk for gastric cancer in heavy- and binge-drinking subjects were also present in subjects not infected by CagA- or VacA-secreting H. pylori.Conclusions:Heavy and binge alcohol consumption is an important risk factor related to an increasing incidence of gastric cancer in a population not infected by H. pylori.

Optical measurements of gas temperatures in atmospheric pressure RF cold plasmas

This work was supported by grant No. R01-2000- 00254 fromthe Korea Science and Engineering Foundation.

Development of a compact helicon ion source for neutron generators

A compact helicon ion source has been designed for a neutron generator. Energetic deuterium beams of 120 keV from this ion source will be directed onto a Ti-coated copper target where D–D nuclear fusion reactions take place and generate 108 n/s of neutrons. High-density radio frequency (rf) plasma sources such as a helicon plasma source, known for its highest efficiency of generating high-density plasmas, are chosen for the development of a high-current density compact ion source. Highest plasma densities for hydrogen plasmas are obtained at relatively low magnetic fields of 100–300 G although plasma densities of helicon plasmas are well known to be almost linearly dependent on magnetic field strength. With Nagoya type III antenna, plasma densities of up to 2×1011 cm−3 are obtained with 1.1 kW rf power at the frequency of 13.56 MHz. With the prototype helicon ion source, hydrogen beam currents of up to 44 mA at 23 kV have been extracted in continuous wave operations with the beam current density of 28.5 m...

Effects of discharge chamber length on the negative ion generation in volume-produced negative hydrogen ion source

In a volume-produced negative hydrogen ion source, control of electron temperature is essential due to its close correlation with the generation of highly vibrationally excited hydrogen molecules in the heating region as well as the generation of negative hydrogen ions by dissociative attachment in the extraction region. In this study, geometric effects of the cylindrical discharge chamber on negative ion generation via electron temperature changes are investigated in two discharge chambers with different lengths of 7.5 cm and 11 cm. Measurements with a radio-frequency-compensated Langmuir probe show that the electron temperature in the heating region is significantly increased by reducing the length of the discharge chamber due to the reduced effective plasma size. A particle balance model which is modified to consider the effects of discharge chamber configuration on the plasma parameters explains the variation of the electron temperature with the chamber geometry and gas pressure quite well. Accordingly, H(-) ion density measurement with laser photo-detachment in the short chamber shows a few times increase compared to the longer one at the same heating power depending on gas pressure. However, the increase drops significantly as operating gas pressure decreases, indicating increased electron temperatures in the extraction region degrade dissociative attachment significantly especially in the low pressure regime. It is concluded that the increase of electron temperature by adjusting the discharge chamber geometry is efficient to increase H(-) ion production as long as low electron temperatures are maintained in the extraction region in volume-produced negative hydrogen ion sources.

Development of a High-Current Helicon Ion Source With High Monatomic Fraction for the Application of Neutron Generators

A high-current helicon ion source has been developed for neutron generator application. High-density plasmas with high electron temperatures are generated by launching helicon waves with a half-helical antenna in various magnetic field configurations. Helicon plasmas with high power efficiency are favorable in building ion sources with high current density and high monatomic ion beam fraction that are required for compact neutron generators. A maximum hydrogen beam current of 50 mA is extracted at 34 kV from the helicon plasma source with 1.9-kW RF power at 13.56 MHz. High current densities of 212 mA/cm2 and high atomic fractions of up to 94% are achieved with this source. These measured beam parameters are mostly consistent with plasma parameters, except for unusually high monatomic beam fraction, which may be due to the existence of energetic electrons in helicon plasmas.

New method of high brightness ion extraction based on bias electrode

It is well known that beam brightness can be enhanced with smaller extraction aperture in plasma ion sources. Reducing aperture size to micrometer scale, however, decreases beam currents significantly since the extraction field cannot be penetrated into the plasma source. In this article, a novel extraction method based on bias electrode is proposed and demonstrated by observing the existence of high current mode with 100μm aperture diameter. Ion current with a positively biased electrode is increased by an order of magnitude from that of the nonbiased case. Locally converging electrons near positively biased electrode are thought to be the main cause of the high current mode.

Design of a far-infrared interferometer/polarimeter system for Korea Superconducting Tokamak Advanced Research

A single-channel vertical interferometer system and a multichannel tangential interferometer/polarimeter system will be constructed on the Korea Superconducting Tokamak Advanced Research device. A vertical system will be used mainly for a density feedback control and a tangential system will be used for getting electron density profile along the radial direction of plasma. Three 118.8 μm methanol lasers optically pumped by 9.7 μm carbon dioxide lasers are implemented as beam sources. The optical system including optics inside the retractable cassette has been designed in the consideration of long beam paths in a narrow diagnostics port. In addition to the shifted phase compensation, focusing mirrors will be used to minimize the deflection error since large deflection of the tangential beam is expected in such a long beam path.