Estimation of dispersion curves of water-loaded structures by using approximated acoustic mass

For coupled structures surrounded by heavy fluids, it is difficult to obtain dispersion curves from an eigenvalue analysis, because the external fluid term in the coupled equation includes transcendental functions for frequency and wavenumber. Thus, in this study, the acoustic mass of the external fluid was approximated as a function of frequency or wavenumber only. The coupled equation can then be used to calculate eigenvalues, and can estimate dispersion curves from an eigenvalue analysis. Because of this assumption, those dispersion curves will contain errors. Accordingly, those errors were evaluated in this study through a comparison with a dispersion curve derived from forced responses. The acoustic mass was also evaluated for a water-loaded plate; this can be formulated theoretically. As a result, the acoustic mass is less sensitive to frequency changes than wavenumber changes, and using the fluid term defined at a low frequency has advantages when estimating the dispersion curve. Finally, the generality of the proposed method was identified through the application for a submerged cylindrical shell.

Modification to the accelerator of the NBI-1B ion source for improving the injection efficiency

Minimizing power loss of a neutral beam imposes modification of the accelerator of the ion source for further improvement of the beam optics. The beam optics can be improved by focusing beamlets. The injection efficiencies by the steering of ion beamlets are investigated numerically to find the optimum modification of the accelerator design of the NBI-1B ion source. The beam power loss was reduced by aperture displacement of three edge beamlets arrays considering power loadings on the beamline components. Successful testing and operation of the ion source at 60 keV/84% of injection efficiency led to the possibility of enhancing the system capability to a 2.4 MW power level at 100 keV/1.9 μP.

Development of internal magnetic probe for current density profile measurement in Versatile Experiment Spherical Torus

An internal magnetic probe using Hall sensors to measure a current density profile directly with perturbation of less than 10% to the plasma current is successfully operated for the first time in Versatile Experiment Spherical Torus (VEST). An appropriate Hall sensor is chosen to produce sufficient signals for VEST magnetic field while maintaining the small size of 10 mm in outer diameter. Temperature around the Hall sensor in a typical VEST plasma is regulated by blown air of 2 bars. First measurement of 60 kA VEST ohmic discharge shows a reasonable agreement with the total plasma current measured by Rogowski coil in VEST.

Development of a novel radio-frequency negative hydrogen ion source in conically converging configuration

Volume-produced negative ion source still requires enhancement of current density with lower input RF (radio-frequency) power in lower operating pressure for various applications. To confirm recent observation of efficient negative ion production with a short cylindrical chamber with smaller effective plasma size, the RF-driven transformer-coupled plasma H(-) ion source at Seoul National University is modified by adopting a newly designed quartz RF window to reduce the chamber length. Experiments with the reduced chamber length show a few times enhancement of H(-) ion beam current compared to that extracted from the previous chamber design, which is consistent with the measured H(-) ion population. Nevertheless, decrease in H(-) ion beam current observed in low pressure regime below ∼5 mTorr owing to insufficient filtering of high energy electrons in the extraction region needs to be resolved to address the usefulness of electron temperature control by the change of geometrical configuration of the discharge chamber. A new discharge chamber with conically converging configuration has been developed, in which the chamber diameter decreases as approaching to the extraction region away from the planar RF antenna such that stronger filter magnetic field can be utilized to prohibit high energy electrons from transporting to the extraction region. First experimental results for the H(-) ion beam extraction with this configuration show that higher magnetic filter field makes peak negative beam currents happen in lower operating pressure. However, overall decrease in H(-) ion beam current due to the change of chamber geometry still requires further study of geometrical effect on particle transport and optimization of magnetic field in this novel configuration.

Prevalence of narcolepsy-cataplexy in Korean adolescents

BACKGROUND

Narcolepsy typically begins between adolescence and early adulthood causing severe neuropsychiatric impairments, but few prevalence studies are available on adolescent narcoleptics. In the present study, we investigated the prevalence of narcolepsy-cataplexy in adolescents.

METHODS

In total 20,407 students, aged 14-19 years, participated in this study. Ullanlinna Narcolepsy Scale (UNS) was applied to all subjects and those with a UNS score of > or =14 were contacted by phone for semi-structured interview. Subjects then suspected of having narcolepsy participated in a laboratory investigation, which included polysomnography and HLA typing, or were interviewed in detail by telephone.

RESULTS

Three subjects were finally diagnosed as narcolepsy with cataplexy and seven subjects might be diagnosed as narcolepsy without cataplexy. Among three narcoleptics with cataplexy, two subjects were HLA-DQB1*0602 and DRB1*1501 positive, but one subject had no test of HLA typing. The prevalence of narcolepsy with cataplexy in Korean adolescence was thus determined to be 0.015% (95% confidence interval = 0.0-0.0313%).

CONCLUSION

This epidemiologic study is the first of its type on adolescent narcolepsy to use the International Classification of Sleep Disorders, 2nd edition (ICSD-2) diagnostic criteria. Considering those cases with an onset after adolescence were not included, the prevalence of narcolepsy with cataplexy determined in the present study is comparable with that of other studies in adults.

Cloning of genes specifically expressed in rice embryogenic cells

We have examined differences in gene expression pattern between embryogenic callus (EC) and nonembryogenic callus (NEC) derived from mature seed embryo of rice (Oryza sativa L. cv Donggin). Three EC-specific transcripts were identified by differential display of amplified cDNAs. Specific expression of two partial cDNAs, designated as REC1 and REC2, respectively, was confirmed by a northern blot analysis. Partial nucleotide sequence of the clone REC1 showed no homology with any known genes, but partial amino acid sequence deduced from the clone REC2 exhibited 55-82% homology with nickel-cobalt-resistant proteins identified from a bacterium, Alcaligenes eutrophus CH34.