178 research outputs found
Enhancement in out-coupling efficiency of flexible organic light emitting diode using metallic nano-hole transparent electrode
No full textCrystallization behaviour of co-sputtered Cu2ZnSnS4 precursor prepared by sequential sulfurization processes
No full textCu2ZnSnS4 (CZTS) thin films were prepared by the sequential sulfurization of a co-sputtered
precursor with a multitarget (Cu, ZnS, and SnS2) sputtering system. In order to investigate the
crystallization behaviour of the thin films, the precursors were sulfurized in a tube furnace at
different temperatures for different time durations. The Raman spectra of the sulfurized thin
films showed that their crystallinity gradually improved with an increase in the sulfurization
temperature and duration. However, transmission electron microscopy revealed an unexpected
result—the precursor thin films were not completely transformed to the CZTS phase and
showed the presence of uncrystallized material when sulfurized at 250–400 C for 60 min and
at 500 C for 30 min. Thus, the crystallization of the co-sputtered precursor thin films showed
a strong dependence on the sulfurization temperature and duration. The crystallization
mechanism of the precursor thin films was understood on the basis of these results and has
been described in this paper. The understanding of this mechanism may improve the standard
preparation method for high-quality CZTS absorber layers.123301sciescopu
Facile synthesis of manganese (II)-doped ZnSe nanocrystals with controlled dimensionality
No full text© 2019 Author(s).Doping is one of the key technologies in modern semiconductor science and industry. However, the synthetic control of doped nanocrystals is difficult to achieve. Here, we report the facile synthesis of manganese (II) doped ZnSe nanocrystals with controlled dimensionality. A strong Lewis acid-base reaction using air-stable and environmentally friendly metal chlorides as precursors can readily produce a large amount of quantum-confined ZnSe:Mn2+ nanocrystals. A combination of primary and secondary amines is used to control the synthetic chemistry, which enables the shape of the doped nanocrystals to be controlled. The final doping concentration of the products can be finely tunable, which is critical for carrier relaxation dynamics. It turns out that the threshold doping level for the maximum photoluminescence intensity of doped nanocrystals highly depends on their shape. Furthermore, this simple synthetic method is extendable to obtain various Mn2+-doped II-VI semiconductor nanocrystals such as CdS:Mn2+ and ZnS:Mn2+. Our study will facilitate the fundamental understanding of the doped semiconductor nanocrystals with different shapes, which is potentially useful for a wide range of applications such as lighting, photocatalysis, and bioimaging11sciescopu
sj-docx-1-wso-10.1177_17474930231159779 – Supplemental material for Gender differences in mortality and long-term functional outcomes after first-ever ischemic stroke: A prospective cohort study
No full textSupplemental material, sj-docx-1-wso-10.1177_17474930231159779 for Gender differences in mortality and long-term functional outcomes after first-ever ischemic stroke: A prospective cohort study by Sang Moon Yun, Seyoung Shin, Won Hyuk Chang, Deog Young Kim, Jongmin Lee, Min Kyun Sohn, Min-Keun Song, Yong-Il Shin, Yang-Soo Lee, Min Cheol Joo, So Young Lee, Junhee Han, Jeonghoon Ahn, Gyung-Jae Oh and Yun-Hee Kim in International Journal of Stroke</p
Phase separation and structure formation in gadolinium based liquid and glassy metallic alloys
No full textIn this PhD research the liquid-liquid phase separation phenomena in Gd-based alloys was investigated in terms of phase equilibria, microstructure formation upon quenching the melt and corresponding magnetic properties of phase-separated metallic glasses. The phase diagrams of the binary subsystems Gd-Zr and Gd-Ti were experimentally reassessed. Especially the phase equilibria with the liquid phase could be determined directly by combining in situ high energy synchrotron X-ray diffraction with electrostatic levitation of the melt. The Gd-Zr system is of eutectic type with a metastable miscibility gap. The eutectic composition at 18 ± 2 at.% Zr, the liquidus line and the coexistence of bcc-Zr and bcc-Gd at elevated temperature could be determined. The Gd-Ti system is a monotectic system. The experimental observations in this work led to improved new Gd-Zr and Gd-Ti phase diagrams.
The phase equilibria of the ternary Gd-Ti-Co system were analyzed for two alloy compositions. The XRD patterns for molten Gd35Ti35Co30 gave direct evidence for the coexistence of two liquid phases formed by liquid-liquid phase separation. The first experimental and thermodynamic assessment of the ternary Gd–Ti–Co system revealed that the stable miscibility gap of binary Gd–Ti extends into the ternary Gd–Ti–Co system (up to about 30 at.% Co).
New phase-separated metallic glasses were synthesized in Gd-TM-Co-Al (TM = Hf, Ti or Zr) alloys. The microstructure was characterized in terms of composition and cooling rate dependence of phase separation. Due to large positive enthalpy of mixing between Gd on the one side and Hf, Ti or Zr on the other side, the alloys undergo liquid-liquid phase separation during rapid quenching the melt. The parameters determining the microstructure development during phase separation are the thermodynamic properties of the liquid phase, kinetic parameters and quenching conditions. By controlling these parameters and conditions the microstructure can be tailored both at microscopic and macroscopic length scales. This includes either droplet-like or interconnected microstructures at the microscopic level and glass-glass or glass-crystalline composites at the macroscopic level.
Essential parameter for the quenched in microstructure is the temperature dependence of liquid-liquid phase separation, which is determined by the chemical composition of the alloy: on the one hand, earlier and/or later stages of spinodal decomposition or almost homogeneous glassy states are obtained if the critical temperature of miscibility gap Tc is close to the glass transition temperature Tg; and on the one hand, coarsening and secondary precipitations of the liquids are obtained if Tc is much higher than Tg. Finally, the influence of the microstructure developed by phase separation on their magnetic properties had been investigated. The saturation magnetization σS depends on the overall amount of Gd atoms in the alloys and is not remarkably affected by phase separation processes. The Curie temperature TCurie of the magnetic transition is influenced by the changed chemical composition of the Gd-rich glassy phases compared to that of monolithic Gd-Co-Al glasses.In dieser Doktorarbeit wurde die flüssig-flüssig Phasenentmischung von Gd-basierten Legierungen hinsichtlich der Phasengleichgewichte, der Gefügeentwicklung während der Schmelzabschreckung und dazugehöriger magnetischer Eigenschaften, untersucht.
Die Zustandsdiagramme der binären Untersysteme Gd-Zr undGd-Ti wurden experimentell ermittelt.. Insbesondere konnten die Phasengleichgewichte mit der flüssigen Phase mittels in-situ Röntgenbeugungsmessunngen an elektrostatisch levitierten Schmelzen direkt, bestimmt werden. Das Gd-Zr System stellt ein ein eutektisches Phasendiagram dar und besitzt eine metastabile Mischungslücke. Die eutektische Zusammensetzung wurde mit 18 ± 2 at.%Zr bestimmt und der Verlauf der Liquiduslinie bei erhöhten Temperaturen wurde experimentell ermittelt. Experimentell wurde die Koexistenz von kubisch-raumzentrierten Zr und Gd in einem Bereich bei hohen Temperaturen nachgewiesen. Das Gd-Ti-System ist von monotektischer Art. Die experimentellen Beobachtungen dieser Arbeit trugen wesentlich zur Verbesserung der Beschreibung der Phasendiagaramme Gd-Zr- und Gd-Ti-Phasenbei.
Die Phasengleichgewichte des ternären Gd-Ti-Co-Systems wurde anhand zweier Legierungszusammensetzungen untersucht. Die Röntgenbeugungsdiffraktogramme der geschmolzenen Legiereung Gd35Ti35Co30 sind ein direkter Beleg für die Koexistenz zweier flüssiger Phasen, aufgrund der flüssig-flüssig Phasenentmischung. Die erste experimentelle und thermodynamische Auswertung des ternären Gd-Ti-Co-Systems zeigt, dass sich die stabile Mischungslücke des binären Gd-Ti-Systems ins ternäre Gd-Ti-Co-System bis zu ungefähr 30 at.% Co erstreckt.
Es wurden neue Gd-TM-Co-Al (TM = Hf, Ti oder Zr)-basierte metallische Gläser, die separierte Phasen besitzen, hergestellt. Ihr Gefüge wurden hinsichtlich Zusammensetzung- und Abkühlratenabhängigkeit der Phasenentmischung charakterisiert. Aufgrund der großen positiven Mischungsenthalpie zwischen Gd auf der einen und Hf, Ti oder Zr auf der anderen Seite, weisen diese Legierungen eine flüssig-flüssig Phasenentmischung während der Abschreckung aus der Schmelze auf. Die Einflussgrößen, die die Gefügeentwicklung während der Phasenentmischung bestimmen, sind die thermodynamischen Eigenschaften der flüssigen Phase, die kinetische Parameter und die Abschreckbedingungen. Indem diese Parameter und Bedingungen kontrolliert werden, kann das Gefüge auf makro- sowie mikroskopischer Längenskala maßgeschneidert werden. Dies beinhaltet entweder tropfenförmige oder miteinander verbundene Gefüge auf einer mikroskopischen Skala und Glas-Glas oder Glas-Kristall Komposite auf einer makroskopischen Längenskala.
Ein wesentlicher Parameter für das abgeschreckte Gefüge ist die Temperatur-Abhängigkeit der flüssig-flüssig Phasenentmischung, die durch die chemische Zusammensetzung der Legierung bestimmt wird. Frühere und/oder spätere Stadien der spinodalen Entmischung oder nahezu homogene amorphe Zustände können abhängig von dem Temperaturunterschied zwischen kritischer Temperatur der flüssig-flüssig Phasenentmischung und der Glasübergangstemperatur erhalten werden. Wenn die kritische Temperatur der Mischungslücke, Tc, viel höher ist als die des Glasübergangs, Tg, können makroskopische Vergröberungen der tropfenförmigen Verteilung der flüssigen Phase und sekundäre flüssige oder kristalline Ausscheidungen in den gebildeten amorphen Phasen erhalten werden.
Durch die Phasenentmischung und die erhaltenen heterogenen Gefüge werden die magnetischen Eigenschaften beeinflusst.. Die Sättigungsmagnetisierung,σS, hängt von der gesamten Anzahl der Gd-Atome der Legierung ab und wird nicht bemerkenswert vom Phasenentmischungsprozess beeinflusst. Die Curie Temperatur TCurie wird im Vergleich zu monolithischen Gd-Co-Al Gläsern, und abhängig von der chemischen Zusammensetzung der Gd-reichen Phase, verändert
OTFS 시스템을 위한 시간-주파수 영역 파일럿 배치 및 저복잡도 채널 추정 기법
No full text학위논문(석사) - 한국과학기술원 : 전기및전자공학부, 2025.2,[iv, 40 p. :]Recently, the Orthogonal Time Frequency Space (OTFS) modulation has been introduced as a novel waveform to substitute its classical counterpart, the orthogonal frequency division multiplexing (OFDM).
The main rationale is that the OFDM has shown weakness in high-mobility scenarios due to the Doppler effect.
The OTFS addresses the issue by embedding data symbols in the delay-Doppler (DD) domain lattice and spreading them using the Symplectic Finite Fourier Transform (SFFT).
The channel model of interest in the OTFS study is known to be sparse in the DD domain, which is a desirable characteristic since it promotes an intuitive approach in solving the channel estimation problem.
The problem can be viewed as equivalent to finding positions and channel coefficients of channel taps in the DD domain.
In this thesis, we propose a low-complexity channel estimation technique for OTFS systems assuming channels with integer delays and fractional Dopplers.
Specifically, we present methods for generating pilots in the time-frequency (TF) domain and estimating the channel parameters using successive interference cancellation (SIC) and removing the pilots.
The pilot removal process is treated separately from the channel estimation complexity analysis.
Finally, we evaluate the proposed scheme and compare it with previously proposed TF domain OTFS channel estimation techniques.한국과학기술원 :전기및전자공학부
Aerodynamic analysis for camber effect in vertical wind turbine system
No full textThe Vertical Axis Wind Turbine (VAWT) has advantages over Horizontal Axis Wind Turbine (HAWT) that it allows less chance to be degraded independent of wind direction and turbine can be operated even at the low wind speed. The objective of this study is to analyze aerodynamics of the VAWT airfoil and investigate the ideal shape of airfoil, more specifically cambers. The analysis of aerodynamic characteristics with various cambers has been performed using numerical simulation with CFD software. As the numerical simulation discloses local physical features around wind turbine, aerodynamic performance such as lift, drag and torque are computed for single airfoil rotation and multiple airfoil rotation cases. Through this study more effective airfoil shape is suggested based vortex-airfoil interaction studies. Copyright �� 2011 by ASME
Employment Shift in Response to a Technology Shock: An Analysis of Two Rigidities and Two Agents
No full textThis paper examines the relationship between a technology shock and employment, considering price, wage rigidities, and heterogeneous agents. To explore this relationship, we utilized a Dynamic Stochastic General Equilibrium (DSGE) model, incorporating households with varying savings rates. For empirical validation, we conducted a Structural Vector Autoregression (SVAR) analysis using data from two economies with distinct savings patterns—the United States and China. This approach allowed us to assess the impact of technology shocks on employment dynamics across different savings environments. Under these conditions, we observe that the effect of technology on aggregate employment is initially positive. Still, it gradually decreases in the mid-term, eventually switching to a negative impact before slowly recovering to equilibrium. The reason for this phenomenon depends on (i) the magnitude of fluctuations in price and wage, precisely, which variable’s fluctuations have a greater magnitude, and (ii) which effect, between income effect and substitute effect, is preferred by restricted and unrestricted households. Due to (i), real wages change, and because of (ii), households make different labor supply decisions, leading to fluctuations in employment in response to technology shocks
Modulation of immune cells with mRNA nanoformulations for cancer immunotherapy
No full textThe global adaptation of mRNA vaccines to protect against the COVID-19 pandemic was a major interdisciplinary milestone, demonstrating the potential of combining mRNA applications with nanotechnology. This innovative strategy holds great promise as an improved therapeutic modality for cancer immunotherapy, as further development could facilitate targeted mRNA delivery to specific immune cells and enable manipulation of effector functions. Toward this, researchers have made substantial efforts to modulate various immune cell types, including lymphoid organ dendritic cells for cancer vaccines, peripheral blood lymphocytes for in situ T-cell therapy, and macrophages in the tumor microenvironment to restore antitumor functions. Here, we highlight recent advances in mRNA nanoformulations for cancer immunotherapy, emphasizing strategies for target cell engagement in different immunological sites.
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