Analyzing Spatio-temporal Patterns of Epileptic EEG Signals by Dynamic Mode Decomposition (Mathematical study on Epilepsy)

In this work, we apply a dynamic mode decomposition (DMD) to epileptic EEG data to figure out the spatio-temporal patterns in the data. It is found that some patterns with high frequency have direct influence on the epileptic seizure, and instantaneously capture the abnormal patterns of the neuron firing with high precision. We prepare an ictal and interictal EEG data for an epileptic patient, and investigating the dyamics of the DMD modes captured by the proposed algorithm for the windowed EEG signals. From the results we conclude that the DMD modes extracted from the EEG signals can be useful for analyzing and understanding the dynamics of the epileptic EEG data

ESTIMATING THE CONVERGENCE RATE OF FUNCTIONAL ITERATIONS FOR SOLVING QUADRATIC MATRIX EQUATIONS ARISING IN HYPERBOLIC QUADRATIC EIGENVALUE PROBLEMS (Study on Nonlinear Analysis and Convex Analysis)

We consider Bernoulli's method for solving quadratic matrix equations (QMEs) having form Q(X) = AX^2 +BX+ C = 0 arising in hyperbolic quadratic eigenvalue problems (QEPs) and quasi-birth-death problems (QBDs) where A, B, C ∈ R^[m×m] satisfy Esenfeld's condition [8]. First, we analyze the exsistence of a solution and the convergence of the methods. Second, we sharpen bounds of the rates of convergence. Finally, in numerical experimentations, we show that the modified bounds give appropriate estimations of the numbers of iterations

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School of Energy and Chemical Engineering (Energy Engineering)My MS research has focused on light-emitting diodes (LEDs) devices based on perovskite nanocrystals (PeNCs). All-inorganic PeNCs are promising material for optoelectronic devices due to their easily tunable bandgap, narrow full width at half maximum (FWHM), and high photoluminescence (PL) quantum yield. Moreover, all-inorganic perovskite material has better stability than the other perovskite material that employs hybrid or organic part at A site of perovskite. These outstanding physical properties caused lot of interest in PeNCs for LEDs devices. To make highly efficient LEDs devices, there are several important factors. Those are smooth film morphology, energy band alignment for low charge injection barrier, and charge balance between hole and electron. Especially, perovskite material has low exciton binding energy (Eb), therefore, confining electron and hole into nanocrystals is very important to make exciton. By considering these factors, a lot of research is going on. However, blue-emitting PeNCs have resulted lower quantum yield compared to red or green-emitting PeNCs due to their large bandgap and anion segregation. To achieve commercialization of PeNCs for future display, white LEDs are indispensable, therefore, great development of blue-emitting LEDs is required. From this point of view for high-efficiency blue LEDs devices, 1,8-diiodooctane (DIO) additive has been used for our research. DIO is added to poly[bis(4-phenyl)(4-butylphenyl)amine] (poly-TPD) solution that is employed in hole transporting layer (HTL) to improve hole injection and passivate trap states between poly-TPD layer and perovskite NC layer. By adopting DIO additive to HTL, external quantum efficiency (EQE) of green PeNCs LEDs was enhanced from 2.89 % to 5.17 % compared to the reference device, and EQE of blue PeNCs LEDs was enhanced from 0.58 % to 1.34 % compared to the reference device.ope

Ferroelectric properties of PZT/BFO multilayer thin films prepared using the sol-gel method

In this study, Pb(Zr0.52Ti0.48)O3/BiFeO3 [PZT/BFO] multilayer thin films were fabricated using the spin-coating method on a Pt(200 nm)/Ti(10 nm)/SiO2(100 nm)/p-Si(100) substrate alternately using BFO and PZT metal alkoxide solutions. The coating-and-heating procedure was repeated several times to form the multilayer thin films. All PZT/BFO multilayer thin films show a void-free, uniform grain structure without the presence of rosette structures. The relative dielectric constant and dielectric loss of the six-coated PZT/BFO [PZT/BFO-6] thin film were approximately 405 and 0.03%, respectively. As the number of coatings increased, the remanent polarization and coercive field increased. The values for the BFO-6 multilayer thin film were 41.3 C/cm2 and 15.1 MV/cm, respectively. The leakage current density of the BFO-6 multilayer thin film at 5 V was 2.52 × 10-7 A/cm2

Reverse Doppler Effect of Sound

We report observation of reverse Doppler effect in a double negative acoustic metamaterial. The metamaterial exhibited negative phase velocity and positive group velocity. The dispersion relation is such that the wavelength corresponding to higher frequency is longer. We observed that the frequency was down-shifted for the approaching source, and up-shifted when the source receded

Relationship between theory of planned behavior factors and optimistic bias and vegetable and fruit intake in college students.

The purpose of this study is to verify the validity of the theory of planned behavior on the vegetable and fruit consumption behavior of college students and to explore the influence of the theory of planned behavior variables on the vegetable and fruit consumption behavior and the role of optimism bias in the relationship. The participants in this study were 249 college students (male: 107, female: 142), and their average age was 20.57 (SD = 2.14) years. In this study, we used a vegetable and fruit consumption frequency list based on Korean nutritional intake standards, the Fruit and Vegetable Module questionnaire, and a questionnaire measuring attitudes toward vegetable and fruit consumption, subjective norms, perceived behavioral control and intention, and optimistic bias. As a result of the analysis, it was verified that it was appropriate to adopt the theory of planned behavior model, which includes a direct path from perceived behavioral control to vegetable and fruit consumption behavior. In hierarchical regression analysis, the Theory of Planned Behavior variables explained about 28.8% of vegetable and fruit consumption behavior, and perceived behavioral control was the strongest predictor, and optimism bias accounted for an additional 1.9% of vegetable and fruit consumption behavior. appeared to explain it. In addition, optimistic bias moderated the relationship between attitude toward vegetable and fruit consumption and vegetable and fruit consumption behavior. Considering the results, it is reasonable to explain vegetable and fruit consumption behavior with the theory of planned behavior, and it was found that optimistic bias plays an important role in the relationship between attitudes toward vegetable and fruit consumption and vegetable and fruit consumption behavior.

Intangible assets investment and firms’ performance: evidence from small and medium-sized enterprises in Korea

While many studies have examined the relationship between investment in intangibles assets and performance in large corporations, current research is lacking in regard to intangible investments in small and medium enterprises (SMEs). This study looks at SMEs in which intangible investments would usually be minor because they tend to consider intangible investment as an inefficient cost and concentrate on investments in tangible assets. This paper aims to contribute to the current literature and suggests that investment in the intangible assets of (human capital, advertising, R&D) is essential for SMEs pursuing superior firm performance. Actual data collected from 173 SMEs in Korea were analyzed employing hierarchical regression methodology. Results indicate that all three intangible resources have a positive effect on a firm’s profitability and value. Interestingly, this research finds that investment in advertising has the most influential impact on a firm’s profitability and value. This study has implications for SMEs in achieving their profitability and value. The results in this study highlight that intangible investment is not a waste of money for SMEs, and that business managers could strategically utilize these three key contributors (human capital, advertising, R&D) and adopt investment in intangible assets to accomplish their managerial goals

Shape optimization of superconducting transmon qubit for low surface dielectric loss

Surface dielectric loss of superconducting transmon qubit is believed as one of the dominant sources of decoherence. Reducing surface dielectric loss of superconducting qubit is known to be a great challenge for achieving high quality factor and a long relaxation time ($T_{1}$). Changing the geometry of capacitor pads and junction wire of transmon qubit makes it possible to engineer the surface dielectric loss. In this paper, we present the shape optimization approach for reducing Surface dielectric loss in transmon qubit. The capacitor pad and junction wire of the transmon qubit are shaped as spline curves and optimized through the combination of the finite-element method and global optimization algorithm. Then, we compared the surface participation ratio, which represents the portion of electric energy stored in each dielectric layer and proportional to two-level system (TLS) loss, of optimized structure and existing geometries to show the effectiveness of our approach. The result suggests that the participation ratio of capacitor pad, and junction wire can be reduced by 16% and 26% compared to previous designs through shape optimization, while overall footprint and anharmonicity maintain acceptable value. As a result, the TLS-limited quality factor and corresponding $T_{1}$ were increased by approximately 21.6%