• Journal of Astronomy and Space Sciences
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• v.36 no.3
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• pp.121-131
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• 2019

The ionospheric mid-latitude trough (IMT) is the electron density depletion phenomenon in the F region during nighttime. It has been suggested that the IMT is the result of complex plasma processes coupled to the magnetosphere. In order to statistically investigate the characteristics of the IMT, we analyze topside sounding data from Alouette and ISIS satellites in 1960s and 1970s. The IMT position is almost constant for seasons and solar activities whereas the IMT depth ratio and the IMT feature are stronger and clearer in the winter hemisphere under solar minimum condition. We also calculated transition heights at which the densities of oxygen ions and hydrogen/helium ions are equal. Transition heights are generally higher in daytime and lower in nighttime, but the opposite aspects are seen in the IMT region. Utilizing the Incoherent Scatter Radar (ISR) electron temperature measurements, we find that the electron temperature in the IMT region is enhanced at night during winter. The increase of electron temperature may cause fast transport of the ionospheric plasma to the magnetosphere via ambipolar diffusion, resulting in the IMT depletion. This mechanism of the IMT may work in addition to the simply prolonged recombination of ions proposed by the traditional stagnation model.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.572-578
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• 2014

In order to overcome small current drivability of a tunneling field-effect transistor (TFET), a TFET using Schottky barrier (SBTFET) is proposed. The proposed device has a metal source region unlike the conventional TFET. In addition, dopant segregation technology between the source and channel region is applied to reduce tunneling resistance. For TFET fabrication, spacer technique is adopted to enable self-aligned process because the SBTFET consists of source and drain with different types. Also the control device which has a doped source region is made to compare the electrical characteristics with those of the SBTFET. From the measured results, the SBTFET shows better on/off switching property than the control device. The observed drive current is larger than those of the previously reported TFET. Also, short-channel effects (SCEs) are investigated through the comparison of electrical characteristics between the long- and short-channel SBTFET.

• Proceedings of KOSOMES biannual meeting
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• 2006.11a
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• pp.31-36
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• 2006

In this paper data of index is acquired by some experts. Then the ambipolar models of Fussy Synthesis Evaluation theory is adopted in this paper which helps to the synthesis analysis of the Aids to Navigation in DaLian port area. At the same time, in accordance with the suggestion of the experts and the real condition, the idiographic implement way is mentioned in the point of view of Quality. The two points of view make the scheme more scientific and feasible. After achieving the status, the project scheme of synthetical alteration to Aids to Navigation in DaLian port area is put forward. It arranges the improved ideas from the different point of view of content, efficiency expectation of Aids to Navigation which gives the reference of the alteration and development of the Aid to Navigation which gives the reference of the alteration and development of the Aids to Navigation in DaLian port area for the future.

• Advances in nano research
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• v.2 no.1
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• pp.1-14
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• 2014

Dislocations are basic crystal defects and represent one-dimensional native nanostructures embedded in a perfect crystalline matrix. Their structure is predefined by crystal symmetry. Two-dimensional, self-organized arrays of such nanostructures are realized reproducibly using specific preparation conditions (semiconductor wafer direct bonding). This technique allows separating dislocations up to a few hundred nanometers which enables electrical measurements of only a few, or, in the ideal case, of an individual dislocation. Electrical properties of dislocations in silicon were measured using MOSFETs as test structures. It is shown that an increase of the drain current results for nMOSFETs which is caused by a high concentration of electrons on dislocations in p-type material. The number of electrons on a dislocation is estimated from device simulations. This leads to the conclusion that metallic-like conduction exists along dislocations in this material caused by a one-dimensional carrier confinement. On the other hand, measurements of pMOSFETs prepared in n-type silicon proved the dominant transport of holes along dislocations. The experimentally measured increase of the drain current, however, is here not only caused by an higher hole concentration on these defects but also by an increasing hole mobility along dislocations. All the data proved for the first time the ambipolar behavior of dislocations in silicon. Dislocations in p-type Si form efficient one-dimensional channels for electrons, while dislocations in n-type material cause one-dimensional channels for holes.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.487-487
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• 2011

Recently graphene has emerged as a fascinating 2D system in condensed-matter physics as well as a new material for the development of nanotechnology. The unusual electronic band structure of graphene allows it to exhibit a strong ambipolar electric field effect with high mobility. These properties lead to the possibility of its application in high-performance transparent conducting films (TCFs). Compared to indium tin oxide (ITO) electrodes, which have a typical sheet resistance of ${\sim}60{\Omega}$/sq and ~85 % transmittance in the visible range (400?900 nm), the CVD-grown graphene electrodes have a higher/flatter transmittance in the visible to IR region and are more robust under bending. Nevertheless, the lowest sheet resistance of the currently available CVD graphene electrodes is higher than that of ITO. Here, we report an ingenious strategy, irradiation of MeV electron beam (e-beam) at room temperature under ambient condition, for obtaining size-homogeneous gold nanoparticle decorated on graphene. The nano-particlization promoted by MeV e-beam irradiation was investigated by transmission electron microscopy, electron energy loss spectroscopy elemental mapping, and energy dispersive X-ray spectroscopy. These results clearly revealed that gold nanoparticle with 10 ~ 15 nm in mean size were decorated along the surface of the graphene after 1.5 MeV-e-beam irradiation. A chemical transformation and charge transfer for the metal gold nanoparticle were systematically explored by X-ray photoelectron spectroscopy and Raman spectroscopy. This approach advances the numerous applications of graphene films as transparent conducting electrodes.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.29.4-30
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• 2010

A VHF meteor radar at King Sejong Station ($162.22^{\circ}S$, $58.78^{\circ}W$), Antarctica has been observing meteors during a period of March 2007-July 2009. We analyzed the height profiles of the observed meteor decay times between 70 and 95 km by classifying strong and weak meteors according to their estimated electron line densities. The height profiles of monthly averaged decay times show a peak whose altitude varies with season in the range of 80~85 km: higher peak in southern spring and summer than in fall and winter. The higher peak during summer is consistent with colder temperatures that cause faster chemical reactions of electron removal, as effective recombination rates measured by rocket experiments. The height profiles of 15-min averaged decay times show a clear increasing trend with decreasing altitude from 95 km to the peak altitude, especially for weak meteors. This feature for weak meteors is well explained by ambipolar diffusion of meteor trails, allowing one to estimate atmospheric temperatures and pressures, as in previous studies. However, the strong meteors show not only significant scatters but also different slope of the increasing trend from 95 km to the peak altitude. Therefore, atmospheric temperature estimation from meteor decay times should be applied for weak meteors only. In this study, we present the simple model decay times to explain the height profiles of the observed decay times and discuss the additional removal processes of meteor trail electrons through the empirical recombination and by icy particles.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.283-287
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• 2005

The slow evolution of global magnetic fields and other dynamical processes in atmospheres of CP magnetic stars lead to the development of induced electric currents in all conductive atmospheric layers. The Lorentz force, which results from the interaction between a magnetic field and the induced currents, may modify the atmospheric structure and provide insight into the formation and evolution of stellar magnetic fields. This modification of the pressure-temperature structure influences the formation of absorption spectral features producing characteristic rotational variability of some spectral lines, especially the Balmer lines (Valyavin et al., 2004 and references therein). In order to study these theoretical predictions we began systematic spectroscopic survey of Balmer line variability in spectra of brightest CP magnetic stars. Here we present the first results of the program. A0p star $\Theta$ Aur revealed significant variability of the Balmer profiles during the star's rotation. Character of this variablity corresponds to that classified by Kroll (1989) as a result of an impact of significant Lorentz force. From the obtained data we estimate that amplitudes of the variation at H$\alpha$, H$\beta$, H$\gamma$ and H$\delta$ profiles reach up to $2.4\%$during full rotation cycle of the star. Using computation of our model atmospheres (Valyavin et al., 2004) we interpret these data within the framework of the simplest model of the evolution of global magnetic fields in chemically peculiar stars. Assuming that the field is represented by a dipole, we estimate the characteristic e.m.f. induced by the field decay electric current (and the Lorentz force as the result) on the order of $E {\~} 10^{-11}$ cgs units, which may indicate very fast (< < $10^{10}$ years) evolution rate of the field. This result strongly contradicts the theoretical point of view that global stellar magnetic fields of CP stars are fossil and their the characteristic decay time of about $10^{10}$ yr. Alternatively, we briefly discuss concurring effects (like the ambipolar diffusion) which may also lead to significant atmospheric currents producing the observable Lorentz force.