• 대한수학회보
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• 제43권4호
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• pp.763-770
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• 2006

Let X be a four-dimensional projective variety defined over the field of complex numbers with only terminal singularities. We prove that if the intersection number of the canonical divisor K with every very general curve is positive (K is almost numerically positive) then every very general proper subvariety of X is of general type in ';he viewpoint of geometric Kodaira dimension. We note that the converse does not hold for simple abelian varieties.

• 조명전기설비학회논문지
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• 제25권7호
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• pp.83-91
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• 2011

Even if smoke, fumes, mist or dust particles are removed by electrostatic precipitators (ESPs), the occurrence of ozone, which is harmful to human body, has to be severely restricted in the indoor environments of hospitals, offices, and workshops. Therefore, the two-stage ESP generating positive corona at the ionizer is typically used because it creates less ozone than the two-stage ESP generating negative corona at the ionizer. In order to predict the collection performance and the optimal design of the two-stage ESP applied to positive high-voltage, particle concentration is experimentally investigated in this paper. In addition, particle motion within the collector section is also numerically analyzed. The positive corona discharge current of the ionizer is found to be affected by the applied voltage in the collector section but less so by the particle concentration. Particle concentration shows a minimum near the high voltage electrode of the collector section. The minimum value of the collection efficiency is almost proportional to gas velocity. When the collector length decreases, the minimum value of the collection efficiency increases. Charged particles entering the collector region are linearly deflected towards the grounded plate by an electric field. From the above experimental and numerical results, two empirical equations on the concentration ratio and the collection efficiency are derived, and are in good agreement with the experimental data.

• 산업기술연구
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• 제25권A호
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• pp.141-149
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• 2005

We investigated numerically the evolutions of several chemical species which are important for film growth and particle generation in the pulsed $SiH_4$ plasmas. During the plasma-on, the $SiH_x$ concentration increases with time mainly by the generation reaction from $SiH_4$, but, during the plasma-off, decreases because of the hydrogen adsorption reaction. During the plasma-on, the concentrations of negative ions increase with time by the polymerization reactions of negative ions and those become almost zero in the sheath regions because of the electrostatic repulsion. During the plasma-off, the concentrations of negative ions decrease with time by the neutralization reactions with positive ions and some negative ions can diffuse toward the sheath regions because there is no electric field inside the reactor. The polymerized negative ions of higher mass can be reduced successfully by using the pulsed plasma process.