Journal of the Korean Physical Society最新文献

The start counter is a scintillator detector designed to measure the reference time of the incident beam for the Large Acceptance Multi-Purpose Spectrometer (LAMPS) experiment at the Rare isotope Accelerator complex for ON-line experiments (RAON). The detector is composed of a plane of plastic scintillator and Multi-Pixel Photon Counter (MPPC) arrays attached to both edges of the scintillator. To understand the performance of the start counter, a simulation framework has been developed using the GENAT4 toolkit, which can simulate the generation and propagation of optical photons. Detailed optical properties of the scintillator and MPPCs are implemented in the simulation for a 5.48 MeV (alpha) beam corresponding to a (^{241})Am radiation source. In this paper, we will report on the development of the simulation framework and its performance, including its application to the 250 MeV/A (^{132})Sn beam as a typical rare isotope beam.

The Sagdeev pseudopotential (SP) method is used to study ion acoustic solitary waves (IASWs) in a warm, magnetized plasma with relativistic electrons. Employing the pseudopotential approach allows for the investigation of solitary wave (SW) structures across arbitrary amplitudes. The study highlights the simultaneous occurrence of compressive (left( {N > 1} right)) subsonic (left( {M < 1} right)) solitons, as well as rarefactive (left( {N < 1} right)) subsonic and supersonic (left( {M > 1} right)) solitons, under specific parametric conditions. Notably, it is seen that as the direction cosine of wave propagation (k_{z}) increases, both the amplitude of SWs and the depth of the potential well decrease. The reduction in amplitude indicates a closer alignment between the magnetic field lines and the direction of wave propagation. The coexistence of compressive subsonic, rarefactive subsonic, and supersonic solitons in this plasma model is a rich and complex phenomenon that has both fundamental and practical implications in plasma physics. It reflects the intricate interplay of nonlinear effects, particle dynamics, and wave propagation in plasmas, with potential applications in both laboratory and astrophysical contexts.

The concept of Chern insulators is one of the most important building block of topological physics, enabling the quantum Hall effect without external magnetic fields. The construction of Chern insulators has been typically through an guess-and-confirm approach, which can be inefficient and unpredictable. In this paper, we introduce a systematic method to directly construct two-dimensional Chern insulators that can provide any nontrivial Chern number. Our method is built upon the one-dimensional Rice–Mele model, which is well known for its adjustable polarization properties, providing a reliable framework for manipulation. By extending this model into two dimensions, we are able to engineer lattice structures that demonstrate predetermined topological quantities effectively. This research not only contributes the development of Chern insulators but also paves the way for designing a variety of lattice structures with significant topological implications, potentially impacting quantum computing and materials science. With this approach, we are to shed light on the pathways for designing more complex and functional topological phases in synthetic materials.

The bacterial flagellar motor is the largest and most complex biological rotary machine that exerts a torque of up to about 1000 pN to propel the swimming of flagellated bacteria. It is embedded in the cell membrane and consists of a 40 nm rotor and about 11 stators. Each stator unit, a torque generating protein complex, is driven by the proton motive force, a proton electrochemical gradient across the inner membrane. However, despite much progress, we lack sufficient evidence of how the ion flow is coupled to motor rotation. Here, we measured the motor speed as a function of the number of stators and found that the number of stators is linearly proportional to the motor speed. Our measurement shows that each stator passes about 24 ions per revolution, indicating that each proton flow can generate torque to drive the motor rotation about 14 degrees which is consistent with 26-fold periodic due to 26 FliG subunits. This result shows that the fixed number of ions yields a constant motor rotation independent of the number of stators and motor speed, indicating proton tight coupling between torque generation and proton flux.

The electromagnetic transition form factors for the (N+gamma ^{*}rightarrow N^{*}) transition between the ground and excited states of nucleons is studied in the framework of the hard-wall model of AdS/QCD. The 5-dimensional equation of motion was solved for the fermion and vector fields. The profile function of the spinor field and bulk-to-boundary propagator of the vector field are presented. The interaction Lagrangian includes other kinds of terms in addition to the minimal coupling term. Using the AdS/CFT correspondence between the generating functions in the bulk and boundary theories, an expression for the transition form factors is obtained from the bulk action for the interaction between the photon and nucleon fields. We consider the (N^{*}(1440,1535,1710)rightarrow N) transitions and plot the Dirac, Pauli and electric, magnetic form factors dependencies on momentum transfer. Also, plots for the helicity amplitudes have been presented and compared to experimental data. The transition radii obtained within the soft-wall model are close to the experimental data for the radii of the nucleons at ground states.

Van der Waals (vdW) two-dimensional semiconductors exhibit excellent optical properties due to their atomically thin thickness and unique band structures. When they are utilized in optoelectronic device applications, the devices show excellent performance as shown for transition metal dichalcogenides and graphene. However, at telecom frequencies, these demonstrations have been largely missing yet. In this study, we demonstrate that trilayer phosphorene pn-diodes can efficiently emit electroluminescence and generate photocurrent at telecom frequencies. Split gates realize electrically tunable pn-diode devices. Under reverse bias, the device shows prominent photocurrent in the photovoltaic mode. Under forward bias, the device shows prominent electroluminescence at the band edge of 0.82 eV. Interestingly, electroluminescence exhibits strong optical anisotropy due to the crystal anisotropy. Our study shows promising potential of trilayer phosphorene for efficient light emitting and photodetection device applications at telecom frequencies.

This article investigates the performance of a 14 nm gate length heterostructure Si_0.5Ge_0.5/Si junctionless gate-all-around (SiGe-JLGAA) device employing SILVACO ATLAS 3D simulator. The proposed device is analyzed in three configurations: underlap, fit, and overlap, and they are compared to a conventional entire region silicon JLGAA structure. First, the choice of x = 0.5 for Ge molar fraction and the device’s physical behavior for all states are discussed. Second, many analog/radio frequency (RF) figures of merit (FoMs) in terms of transconductance (g_m), gate-to-gate capacitance (C_GG), cutoff frequency (f_T), gain bandwidth product (GBP), transit time (τ), and transconductance frequency product (TFP) are investigated. The fit configuration SiGe-JLGAA device demonstrates g_m = 67.4 µS, f_T = 1033 GHz, GBP = 115 GHz, TFP = 4.2 THz/V and τ = 1.3 × 10¹³ s, whereas the corresponding values for a conventional device are 13.5 µS, 354 GHz, 37 GHz, 1.2 THz/V and 5.9 × 10¹³ s, respectively. In addition, the reliability of the proposed device in terms of linearity for the three forms is compared. Finally, using a Verilog-A model in Cadence tool, the applications of the SiGe-JLGAA device in designing two types of inverters, binary and ternary, are demonstrated. The fit form exhibits superior DC and transient characteristics compared to other structures. The proposed device significantly enhances all configurations compared to the conventional JLGAA structure, thereby opening up a wide range of applications in digital circuits.

Terahertz light sources with small size and high output enable a variety of new applications. Free-electron laser (FEL) is the most powerful light source in the terahertz (THz) range with perfect wavelength tunability. However, the size of the FEL facility is too large. We are developing a table-top THz FEL using a small microtron accelerator. Through the development of a high-performance and compact undulator and a new waveguide-mode resonator, we confirmed that an FEL size of 1.5 × 2 m² is possible. One of the reasons we could design the small FEL is because we do not use electromagnets to force the electron beam into and out of the FEL resonator. We have developed an out-coupling mirror of the FEL resonator for a wide spectral range from 0.5 to 1 THz to have a structure in which the electron and THz beam transmit simultaneously without any bending magnets. The out-coupling mirror has wire-grid-polarizer (WGP) structure in the center. This paper discusses optimizing the WGP's parameters like wire thickness and period to get appropriate reflectance and transmittance in the 0.5–1 THz region and has low electron beam loss in the waveguide-based resonator using the COMSOL Multiphysics simulation. Simulations found the optimized value of wire thickness and period as 20 and 100 µm, respectively. We further calculated the TE transmittance of the WGP, which is 1-030% for the optimized values, depending on the frequency, ranging from 0.5 to 1 THz. Experiments using the THz time-domain spectroscopy method validated that the measured results agreed with those of the simulations.

In targets like airplanes, rockets, or missiles, there are both the target and the plume. When tracking the target through imaging optics, the plume can become background depending on the perspective of the optical system. When plumes are in the background, the target image may be obscured by the saturation of the plume signals. In this study, a range-gated short-wave infrared (SWIR) imaging system was considered for the acquisition and tracking of the target against the plume background. The target signal is the illumination laser light reflected from the target and the background signal is the self-radiation of the plume. We considered a method using the illumination laser energy and the detector integration time to increase the target signal and decrease the plume signal. We analyzed the system signal-to-noise ratio (SNR) as a function of the illumination laser energy and the detector integration time. As a result, we derived system design specifications satisfying the SNR greater than 2.5.

Recently, there has been a global societal focus on the management of air pollution. Measurements of air pollution are conducted using various methods depending on the pollutants, including ultraviolet (UV) absorption methods for ozone (O₃) and fluorescence methods for sulfur dioxide (SO₂). However, the conventional silicon-based complementary metal–oxide–semiconductor image sensor (Si-CIS) is not suitable for UV measurements due to the low quantum efficiency (QE) of silicon for UV light. Consequently, different types of detection sensors are used for different air pollutants, leading to limitations in measurement locations and resulting in errors depending on the installation position. To address these limitations, we propose a quantum dot complementary metal–oxide–semiconductor image sensor (QD-CIS) capable of imaging UV light using the energy-down-shift (EDS) mechanism of quantum dots (QDs). The synthesized QDs absorb light at UV wavelengths, convert it into visible blue light through EDS, and emit luminescence. The converted intensity allows the detection of UV intensity by the CIS. Through the designed QD-CIS and UV LED illumination, we measured the sensitivity to changes in the concentrations of the representative air pollutants NO₂ and SO₂. The results showed a sensitivity increase of 6.83 times for NO₂ and 21.39 times for SO₂ compared to conventional CIS. This suggests the potential of UV imaging to overcome these limitations using existing CIS components.