Journal of the Korean Physical Society最新文献

Using the quantum kinetic equation method for electrons in the semi-parabolic plus semi-inverse squared quantum well (SPPSISQW) structure in the presence of external electromagnetic waves, we derived novel analytical expressions for the acousto-magneto-electric (AME) field. In addition, numerical results were conducted to investigate the dependence of the AME field on various parameters, including the frequency of external electromagnetic waves, acoustic wave frequency (omega_{q}), temperature, magnetic field. Notably, the resonance peak position of the AME field remains unaffected by temperature but shifts significantly with electromagnetic wave frequency and magnetic field. The high-frequency electromagnetic wave significantly enhance the AME field, introducing new resonant peaks and modulating the field’s amplitude and position. As the frequency of EMW Ω increases, the resonance peaks shift to higher magnetic field values. The study identifies the cyclotron resonance phenomenon, where the AME field increases sharply at specific magnetic field strengths. This resonance shifts with changes in the electromagnetic wave frequency, indicating a complex interplay between electrons, phonons, and external fields. These findings contribute to perfecting quantum theory and enrich our understanding of the unique properties of SPPSISQW structure, especially highlighting significant differences from conventional bulk semiconductors and other low-dimensional semiconductor structures such as quantum wires and superlattices. Furthermore, the influence of external electromagnetic waves introduces nonlinear effects and distinctive results compared to scenarios without electromagnetic waves, as demonstrated by the results presented in this study.

To address gamma spectrometry on complex-shaped materials when the conventional method based on certified reference materials is impractical, we propose a new 3D-scan-based source modeling method for reflecting geometry of complex-shaped materials. Various complex-shaped materials were selected, scanned with tailored methods depending on the scanned objects, and the scanned 3D data were integrated into the source term models for Monte Carlo simulation. The developed method has been confirmed that all complex-shaped materials thus created can be cast into the Monte Carlo simulation toolkit Geant4 as source terms. It produced mesh deviations of all samples within 1 mm, validating its utility for practical applications. The developed method was experimentally validated using CRM, proving the accuracy of the method. The proposed method enables a comprehensive efficiency calibration for radioactivity analysis of complex-shaped materials without the need for destructive preprocessing.

Boundary layer flow over stretching surfaces has gained major scientific attention because of its importance in industrial and biomedical applications. However, flow over curved surfaces remains largely underexplored. This article leverages the Buongiorno model and Cattaneo–Christov (CC) double diffusion to explore the stagnation point flow of a micropolar fluid along a vertical stretching cylinder. Additional consideration of chemically reactive fluid under activation energy makes the analysis novel and relevant. Similarity transformations are used to convert the governing partial differential equations (PDEs) into a system of ordinary differential equations (ODEs), which are then solved using the fourth-order Runge–Kutta technique with a shooting approach. The numerical solutions provided trends of velocity, microrotation, temperature, concentration, entropy generation, and Bejan number under a multitude of pertinent parameters graphically. The heat and mass transfer rates and skin friction at the boundary were also tabulated. Results indicate that thermophoresis and thermal radiation enhance temperature, while the curvature of the cylinder adversely affects microrotation, but improves skin friction. Thermophoresis raises concentration, but Brownian motion lowers it. The temperature is lowered and raised by thermal and concentration relaxation parameters, respectively. The accuracy of the findings is confirmed by validation against the body of existing literature. Potential uses for this research include tailored medication administration and cancer treatments, including chemotherapy.

GaN epilayers grown on c-plane sapphire substrates were irradiated with different doses of γ-rays ranging from 300 to 3000 krad. From the photoluminescence (PL) measurement, the yellow PL (YL) intensity decreased with increasing the γ-ray irradiation dose. From the deep level transient spectroscopy (DLTS), three defect states of E1, E2, and E5 levels with activation energies of 0.17 ± 0.02, 0.52 ± 0.01, and 0.97 ± 0.02 eV below the conduction band edge were found in the samples. The E1, E2, and E5 levels originated from the defects of nitrogen vacancy (V_N), nitrogen antisite (N_Ga), and interstitial nitrogen (N_i), respectively. With increasing γ-ray doses, the N_t value of N_Ga was increased, while the N_t values of V_N, N_i, V_Ga–N_i complex decreased. Therefore, it was suggested that the yellow PL band originated from the V_Ga–N_i complex.

Over the past few years, Internet of Things (IoT) has surfaced as an effective technology which helps in interconnecting objects and computing devices together. Enormous potential of IoT has helped in providing more convenient and high-quality services for many day-to-day applications. Tangible objects can be connected to internet through IoT which enables rapid reception and transmission of data. Significant advancement of IoT technology further helps in connecting different smart objects via internet as well as facilitates in providing better methods for data interoperability. In many large-scale applications like healthcare monitoring, environment monitoring, smart agriculture, smart cities, smart grids, smart factories etc., IoT is playing a significant role. Machine learning, embedded systems, real-time analytics and sensors have influenced the concept of IoT. IoT sensors help in providing improved communication without the necessity for human-to-human and human-to-computer interface. This article critically analyzes various IoT sensor-based systems used in medical surveillance and in monitoring of air and water quality. The article reviews the state-of-the-art developments, real word application, and key technologies in these domains. The performance of various IoT sensor-driven systems used for monitoring in real time were also meticulously studied.

A micromembrane mechanical resonator was fabricated from stoichiometric silicon nitride. Its resonant motion was actuated using an electrical field gradient force generated by electrodes adjacent to the oscillating structure, eliminating the need for electrodes directly on the movable membrane, thereby preserving a high-quality factor. This method enables investigation of multiple modes of the micromembrane, up to the 32^nd mode with a resonant frequency of 78 MHz, using optical measurement technique. The absence of a substrate beneath the membrane makes the structure compatible with optical cavities. This compatibility is crucial for cavity-optomechanical systems, which require integration of mechanical devices with high-finesse optical cavities. Furthermore, by applying phase-shifted RF signals, symmetric modes at the similar resonant frequency can be separated and analyzed. The high-frequency and multi-mode operation, coupled with the substrate-free design makes this micromembrane resonator a promising candidate for applications in optical signal processing, optical component integration with high-finesse cavities, and exploration of cavity optomechanics.

Cryogen-free superconducting magnets have become increasingly popular in research and industry. In this work, a cryogenic system was developed to realize rapid cooling of copper plate in conduction-cooled superconducting magnet applied to magnetic resonance imaging (MRI) systems. A full three-dimensional method based on the heat conduction and thermal radiation models was used for predicting heat transfer characteristics inside the device, and the effects of structural connection and dimension on initial cool-down time were also investigated. Simulation results indicated that the temperature of the copper sample plate decreased almost linearly with the increase in cooling time at first and then decreased rapidly due to the proliferated thermal conductivity of copper. The number of thermal links has less effect on initial cool-down time when the number exceeds eight. The initial cool-down time is sensitive to the spacing of the two stages of a cryocooler, with increasing efficiency by about 10% as the spacing increases from 80 to 320 mm. The larger cooling power of first-stage thermal anchor could be a key factor in boosting efficiency. The simulation results were in good agreement with the experimental data and had the potential to achieve low energy consumption and high efficiency of cooling of MRI low-temperature superconducting magnet in practical applications.

In the last few decades, studies in various fields of plasma technology have expanded and its application in different processes has increased. Therefore, the achievement of a desirable and practical plasma with specific characteristics is of particular importance. The frequency of the applied voltage is one of the important factors that play a role in the physical and chemical characteristics. In this research, changes in the density of active species produced in an electrical discharge using a dielectric barrier and air working gas have been investigated, from a frequency of 500 Hz to 500 kHz, and by applying a constant voltage of 2 kV, have been investigated. For this purpose, 87 different reactions with specific collision cross-sections were defined in COMSOL Multiphysics. Other parameters, including current–voltage waveform, electric field, species density including ({text{NO}}),({text{OH}}),({text{O}}_{2}^{ + }),({text{O}}_{3}), etc., were evaluated. The results show that under completely identical conditions, the electron temperature distribution changes with increasing applied frequency, and the density of reactive oxygen and nitrogen species (RONS) like (({text{NO}}), ({text{OH}}), ({text{O}}_{3}),..) decreases, but ({text{O}}_{2}^{ + }) shows an increasing trend. It should be noted that the simulation results are in good agreement with the previous experimental and simulation reports. These results offer valuable insights into optimizing plasma parameters for different applications, potentially resulting in better treatment outcomes across a range of therapeutic domains.

Highly efficient and reliable spin- and angle-resolved photoelectron spectroscopy (spin-ARPES) has been developed at the 4A2 beamline of Pohang Light Source II. The spin polarimeters based on exchange scattering by a ferromagnetic target were integrated into a state-of-the-art hemispherical electron analyzer, enabling us to obtain the electronic band structure with a three-dimensional spin polarization character. The figure of merit (FOM) of the spin polarimeter was proven to be higher than those of conventional Mott detectors by two orders. The spin-dependent electron reflectivity spectra of in situ grown ferromagnetic targets were obtained by the use of a kinetic energy control lens and they are utilized to optimize and stabilize the spin detection asymmetry. The overall performance was demonstrated by measuring the spin-ARPES spectra of the Dirac cone of (hbox {Bi}_2 hbox {Se}_3).

Cu–Sb–Se ternary chalcogenide compounds have garnered interest as potential thermoelectric materials because of their low cost and environmental benefits. Among these, Cu₁₂Sb₄Se₁₃ (hakite), Cu₃SbSe₄ (permingeatite), Cu₃SbSe₃ (bytizite), and CuSbSe₂ (pribramite) stand out as promising candidates because of their narrow band gaps and low thermal conductivity. However, Cu₁₂Sb₄Se₁₃ is unstable in its pure form because of a charge imbalance in its structure, where all copper atoms exist in the monovalent state (Cu⁺). This instability restricts its potential for thermoelectric applications. In this study, we sought to stabilize Cu₁₂Sb₄Se₁₃ by partially substituting Fe²⁺ ions for Cu⁺ ions, aiming to compensate for the charge imbalance and synthesize Fe_xCu_12−xSb₄Se₁₃ (0.5 ≤ x ≤ 2). X-ray diffraction analysis revealed that adding Fe led to the formation of bytizite and CuFeSe₂ (eskebornite), with the pribramite phase emerging as the Fe content increased. Thermal analysis using differential scanning calorimetry revealed that for samples with Fe content between x = 0.5 and 1.5, bytizite and permingeatite phases coexisted. In the Fe₂Cu₁₀Sb₄Se₁₃ sample, three phases were identified: bytizite, permingeatite, and pribramite. This suggests that synthesizing hakite through charge compensation with Fe was not feasible, as Fe substitution resulted in multiple phase formations rather than stabilizing the hakite phase. In terms of thermoelectric properties, the FeCu₁₁Sb₄Se₁₃ sample exhibited a power factor of 80 μWm⁻¹K⁻² and a maximum figure of merit (ZT) of 0.14 at 623 K.