Journal of the Korean Physical Society最新文献

This study investigates the structural and dielectric properties of Ba_xSr_1-xSnO₃ (BSSO, x = 0, 0.2, 0.4, 0.6, 0.8) ceramics prepared by the solid-state reaction method. X-ray diffraction and X-ray photoelectron spectroscopy were used to characterize the phase purity and chemical state of the component elements, respectively. Frequency and temperature dependence of the dielectric properties suggest that the dielectric constant and loss are influenced by Ba²⁺ ions doping concentration, reaching an optimal dielectric performance at x = 0.4. The observed dielectric behavior can be explained by the interfacial polarization and dielectric relaxation processes, originated from the existing oxygen vacancies and Sn⁴⁺–Sn²⁺ pairs. These findings provide valuable insights into the potential applications of Ba_xSr_1-xSnO₃ ceramics in electronic devices.

The optical gain factor of a reflective polarizer in a quantum dot (QD)-based edge-lit backlight was investigated for the first time with various optical film combinations. The QD film, containing red and green quantum dots, was excited by 20 blue LEDs arranged near the light guide plate (LGP). The multilayer-type reflective polarizer significantly altered the color properties of the QD backlight by enhancing QD film excitation through its reflective properties. The gain factor was nearly two when only a single QD film was placed over the LGP without additional optical films, indicating minimal optical loss. However, the gain factor decreased significantly with the addition of prism sheets, likely due to the formation of a strong optical cavity between the bottom reflector and the prism grooves. This suggests that the optical configuration of QD-based backlights should be carefully optimized to account for color changes due to the reflective polarizer and to avoid strong optical cavity effects caused by prism sheets.

This study systematically investigates the effects of nanoparticle (NP) charge and temperature on the thermophysical properties of nanofluids using molecular dynamics simulations. The interaction between charged nanoparticles and solvent particles significantly influences both viscosity and thermal conductivity. The nanoparticles are modeled with varying charges, and their impact on fluid behavior is analyzed in terms of radial distribution functions, viscosity, and thermal conductivity, computed using the Green-Kubo formalism. The findings reveal that increased NP charge leads to reduced aggregation, enhancing dispersion and lowering viscosity, while thermal conductivity exhibits complex behavior, decreasing with NP charge at moderate temperatures but increasing in the supercritical region. Temperature also plays a critical role, with nanofluids demonstrating typical shear-thinning behavior and a distinct phase-dependent response in thermal conductivity. These results provide valuable insights into optimizing nanofluid properties for applications such as coolant systems and lubricants, where both efficient heat transfer and low energy dissipation are crucial. The systematic analysis of charge and temperature effects contributes to a better understanding of the underlying mechanisms governing nanofluid behavior.

Community detection is crucial for understanding complex systems in network science. However, traditional methods often face practical issues due to the variability of the results influenced by resolution parameters. Ensemble-based community detection techniques have been proposed to address this problem by aggregating results from multiple analyses to enhance reliability, and suggested global and local metrics for robust community detection. In this study, we explore the applicability of these ensemble-based techniques to dynamic networks by applying them to simulated networks with evolving community structures. Using the partition inconsistency measure, a global metric assessing overall structural stability, we identified time points where stable community configurations changed. Furthermore, by analyzing the trajectories of membership inconsistency, a local metric quantifying node-level assignment community consistency, we detected nodes that were initially affected by dynamic changes in community structure. These findings demonstrate that ensemble-based community detection methods are effective tools for analyzing dynamic networks. This method has the potential to enhance our understanding of temporal dynamics in complex networks and aid in predicting future states across various domains.

ScAlN, with its ultra-wide band gap and ferroelectric properties, offers promising enhancements for GaN-HEMTs expanding the device-application space. In this work, we report the DC/RF characteristics of lattice-matched Sc_0.18Al_0.82N/GaN-HEMT (SG-HEMT) built on SiC wafer. The SG-HEMT features a graded AlGaN back-barrier (g-AlGaN BB) that enhances the conduction-band (CB) disruption at the AlGaN/GaN interface, improving charge confinement. We examine the impact of Sc_0.18Al_0.82N barrier thickness (T_B) and gate-recess height (T_R) on device performance. As the gate-to-channel distance decreases, transconductance (G_M) increases due to enhanced gate control, and the threshold voltage (V_TH) shifts positively, exhibiting immunity to short-channel effects (SCEs) while preserving a better aspect ratio. Then the scaling behavior of SG-HEMT is explored with different gate lengths (L_G). Besides, the impact of L_SD scaling was studied through comprehensive simulations, and the device-performance metrics were thoroughly analyzed. The findings reveal that a 40 nm L_G device achieves the highest G_M of 423.8 mS/mm, an I_{D_peak} of 2.58 A/mm, and a peak f_T of 239.2 GHz, attributable to the higher polarization of ScAlN and impeded parasitic channel development as an outcome of the g-AlgaN BB, suggesting that lateral scaling is a viable method for enhancing device performance. This work manifests that high current densities can be achieved owing to a high sheet charge density at Sc_0.18Al_0.82N/GaN interface, highlighting the significant potential of SG-HEMTs for enhancing output power at the device level in millimeter-wave (mmw) frequencies and propelling HEMT functionalities.

Recently, there has been progress to resolve the issue regarding the non-existence of the Cauchy horizon inside the static, charged, and spherically symmetric black holes. However, when we generically extend the black holes’ spacetime, they are not just static but can be dynamical, thus the interior of black holes does not remain the same as the static case when we take into account the dynamical evolution of black holes. Hence, the properties of the Cauchy horizon could behave differently in the dynamical case. Then, our aim in this paper is to provide a few constructive insights and guidelines regarding this issue by revisiting a few examples of the gravitational collapse of spherically symmetric charged black holes using the double-null formalism. Our numerical results demonstrate that the inside of the outer horizon is no longer static even in late time, and the inner apparent horizon exists but is not regular. The inner apparent horizon can be distinguished clearly from the Cauchy horizon. The spherical symmetric property of black holes allows the inner horizon to be defined in two directions, i.e., the differentiation of the areal radius vanishes along either the out-going or the in-going null direction. Moreover, the Cauchy horizon can be generated from a singularity. Still, the notion of the singularity can be subtle where it can have a vanishing or non-vanishing areal radius; the corresponding curvature quantities could be finite or diverge, although the curvatures can be greater than the Planck scale. Finally, we show some examples that the “hair” which is associated with the matter field on the inner horizon is not important to determine the existence of the Cauchy horizon; rather, the hair on the outer horizon might play an important role on the Cauchy horizon. Therefore, the dynamic properties of the interior of charged black holes could shed light for us to understand deeply about the Cauchy horizon for the extensions of no-Cauchy-horizon theorems.

Theoretical studies of nuclear structure play a crucial role in understanding the collective properties of nuclei. In this study, we investigated the collective properties of even–even deformed nuclei with simultaneous nuclear rotational and vibrational spectra. From the nuclear Hamiltonian, the low-lying energy levels, and interband and intraband E2 transition probabilities were derived analytically. The Hamiltonian proposed in this study is based on the geometrical model proposed by Bohr and Mottelson representing a typical collective model, and the algebraic model proposed by Arima and Iachello. The energy levels and E2 transition ratios of (^{168})Er were calculated and compared with the experimental data. This theoretical approach effectively described the structure of the deformed nucleus (^{168})Er.

The graphene synthesized by the chemical vapor deposition (CVD) method on Cu foil was transferred onto the SiO₂ substrate with a pre-patterned electrode, and the electrical and thermoelectric properties were measured. Raman spectral analysis and thermoelectric coefficient measurement confirmed that the transferred graphene is mainly composed of single-layer and has p-type properties. The thermoelectric characteristics of the transferred graphene as well as the thermoelectric voltage image mapping in the locally torn, folded or bubbled region of graphene by the scanning probe method using the thermoelectric phenomenon were confirmed on a micro-scale.

Reputation is not just a simple opinion that an individual has about another, but a social construct that emerges through communication. Despite the huge importance in coordinating human behavior, such a communicative aspect has remained relatively unexplored in the field of indirect reciprocity. In this work, we bridge the gap between private assessment and public reputation. We begin by clarifying what we mean by reputation and argue that the formation of reputation can be modeled by a bi-stochastic matrix, provided that both assessment and behavior are regarded as continuous variables. By choosing bi-stochastic matrices that represent averaging processes, we show that only four norms among the leading eight, which judge a good person’s cooperation toward a bad one as good, will keep cooperation asymptotically or neutrally stable against assessment error in a homogeneous society where every member has adopted the same norm. However, when one of those four norms is used by the resident population, the opinion averaging process allows neutral invasion of mutant norms with small differences in the assessment rule. Our approach provides a theoretical framework for describing the formation of reputation in mathematical terms.

We report a simple method for fabricating a SnO₂ nanowire (NW) cotton-based ultraviolet (UV) photodetector. SnO₂ NW cotton was synthesized by thermal chemical vapor deposition with SnO powder. Ag paste was coated onto the surface of the SnO₂ NW cotton to serve as the electrode. The performance of the photodetector was evaluated upon UV light exposure at a wavelength of 254 nm, with a photo-to-dark-current ratio of 7.9 × 10⁵, photoresponsivity of 1.141 × 10³ A/W, and specific detectivity of 9.0 × 10¹⁵ Jones. The spectral photoresponsivity was also determined in the 200–600 nm wavelength range. The results showed a maximum responsivity at 270 nm and a cutoff edge wavelength of 360 nm, exhibiting the characteristics of a visible-blind UV photodetector. In addition, self-powered capability with a photocurrent of 2.3 nA was demonstrated at a nominal zero bias.