In this article, we develop a novel large volatility matrix estimation procedure for analyzing global financial markets. Practitioners often use lower-frequency data, such as weekly or monthly returns, to address the issue of different trading hours in the international financial market. However, this approach can lead to inefficiency due to information loss. To mitigate this problem, our proposed method, called Structured Principal Orthogonal complEment Thresholding (S-POET), incorporates observation structural information for both global and national factor models. We establish the asymptotic properties of the S-POET estimator, and also demonstrate the drawbacks of conventional covariance matrix estimation procedures when using lower-frequency data. Finally, we apply the S-POET estimator to an out-of-sample portfolio allocation study using international stock market data.

We investigated potential nosocomial aerosol transmission of severe fever with thrombocytopenia syndrome virus (SFTSV) with droplet precautions. During aerosol generating procedures, SFTSV was be transmitted from person to person through aerosols. Thus, airborne precautions should be added to standard precautions to avoid direct contact and droplet transmission.

A polymer, which by pyrolysis transforms into Al–C–N–(O) ceramics, was synthesized from trimethylamine alane and cyan amide, and its applicability as a sintering additive for Si3N4 was investigated. Si3N4 powders were mixed with the precursor by treatment with organic slurries of the precursor to induce the homogeneous distribution of the additive. The green-bodies were pretreated in air or NH3 at 800 °C to control the chemical composition of the additive, through which the densification of Si3N4 could be improved. Dense samples with very fine grains (<2 μm) were obtained after sintering at 1600 °C in 0.1 MPa N2. Besides silicon nitride, submicrometer silicon carbide particles were observed in the samples, indicating that this procedure (i.e., the use of this novel sintering additive) also allows for the fabrication of SiC–Si3N4 composites.

In the thin film transistor fabrication process, tin doped indium oxide (ITO) or zinc doped indium oxide (IZO) film can be easily exposed to hydrogen-containing plasma during the deposition of silicon nitride (SiNx) film. By this exposure, ITO or IZO can be easily reduced into its corresponding metallic element such as indium, which degrades the optical transmittance and the conductivity. In this study, SiNx was deposited onto ITO or IZO film, and the oxygen reduction of ITO or IZO during PECVD SiNx deposition was analyzed to clarify this phenomenon. The oxygen reduction during PECVD SiNx deposition is mainly induced by decomposed NH3 gas. However, the progress of ITO reduction is different from that of IZO reduction, due to the different atomic composition of In2O3 in the composite and the different critical temperature of reduction initiation between indium oxide, tin oxide, and zinc oxide.

The effects of the active and passive protection mechanisms of powder beds on the sintering of Si3N4 were investigated. Shrinkage, density, and coloring behavior of sintered samples were analyzed using different compositions and packing conditions of powder beds based on BN and Si3N4 with different additives. Y2O3 additive in the powder bed influences the weight change and phase formation behavior of the samples, although it has a very low vapor pressure at the sintering temperature. When MgO/Y2O3 was used as sintering additives, the packing density and thickness of the powder bed had a much stronger effect than in the case of Al2O3/Y2O3. For the optimization of the powder bed conditions, the vapor pressure and chemical stability of sintering additives at the sintering temperature has to be considered.

Dielectric properties and leakage current characteristics of the Al2O3 thin films, deposited by reactive sputtering at room temperature, have been investigated with variations of the O2 content in the sputtering gas and the film thickness. The Al2O3 films of 10-300 nm thickness were amorphous without depending on the O2 contents of 25-75% in the sputtering gas. Maximum dielectric constant was obtained for the Al2O3 film deposited with the sputtering gas of 50% O2 content. With reduction of the film thickness from 300 nm to 10 nm, dielectric constant decreased from 9.04 to 3.71 and tangent loss increased from 0.0035 to 0.0594, respectively. When the O2 content in the sputtering gas was higher than 50%, the Al2O3 films exhibited no shift of the flatband voltage in C-V curves. The leakage current density increased with increasing the film thickness, and the Al2O3 films thinner than 100 nm exhibited the leakage current densities lower than 10−6 A/cm up to 650 kV/cm.

Pt/Sr0.85Bi2.4Ta2O9/Al2O3/Si structures were prepared for MFIS-FET applications. After depositing Al2O3 film of 10-50 nm thickness by reactive sputtering on Si(100) substrate as a buffer layer, Sr0.85Bi2.4Ta2O9 (SBT) thin film of 400 nm thickness was prepared onto it by metalorganic decomposition process. With annealing at 800°C for 1 hour in oxygen ambient, the 400 nm-thick SBT film exhibited 2Pr of 10.2 μC/cm2 and Ec of 37.5 kV/cm at ±5V. C-V characteristics of the Pt/SBT/Al2O3/Si structures exhibited hysteresis loops due to the ferroelectric switching behavior of the SBT film. When the Al2O3 buffer layer was thicker than 10 nm, the memory window and maximum capacitance of the Pt/SBT/Al2O3/Si structure increased with decreasing the thickness of the Al2O3buffer layer, and the Pt/SBT(400 nm)/Al2O3(10 nm)/Si structure exhibited a memory window of 2.2 V at ±5 V.

Pt/Sr0.85Bi2.4Ta2O9/TiO2/Si structures were prepared with variation of the Sr0.85Bi2.4Ta2O9 (SBT) film thickness for MFIS-FET applications. After depositing TiO2 film of 10 nm thickness by reactive sputtering on Si(100) substrate as a buffer layer, SBT thin film of 210-400 nm thickness was prepared onto it by metal organic decomposition process. Regardless of the SBT film thickness, the Pt/SBT/TiO2/Si structures exhibited clockwise directional hysteresis, indicating well-defined ferroelectric switching behavior of the SBT films. While the memory window of the Pt/SBT/TiO2/Si MFIS structures increased with increasing the SBT film thickness, the maximum capacitance of the Pt/SBT/TiO2/Si MFIS structures decreased with increasing the SBT film thickness. The Pt/SBT(400 nm)/TiO2(10 nm)/Si structure exhibited a memory window of 1.3 V at ±5 V.

Both the wafer fusion and the heteroepitaxy technology were used successfully to obtain high quality GaAs layer on the InP substrate where the lattice mismatch was 3.7 %. The enhancement of the lateral growth rate was a crucial factor for the formation of high quality QWR in the patterned fusion layer. This technique can provide a way of overcoming the limitation of heteroepitaxy caused by misfit problems and its subsequent quality degradation. It is expected that the overgrowth technique on the patterned fusion layer can be applicable to the photonic device fabrication on the other substrate such as Si.