Journal of the Korean Physical Society最新文献

Scanning proton therapy offers advantages over conventional photon therapy due to the Bragg-peak effect and superior dosimetric precision. Compared with passive methods, however, scanning proton therapy tends to exhibit a wider penumbra in the low-energy range. To address this issue, the present study evaluated the effectiveness of a patient-specific aperture collimator (AC) and multi-leaf collimator (MLC) for the line proton scanning treatment system at the Samsung Proton Therapy Center in Korea. The penumbra reduction efficiency of the collimation devices and the neutron dose was assessed through Monte Carlo (MC) simulations. The clinical effectiveness was evaluated dosimetrically and by assessing quality assurance. Through the MC calculation, the AC displayed the highest efficiency in penumbra reduction (43.75% of no collimator’s penumbra width at a depth of 10 cm with a 150 MeV proton beam), while the MLC also presented a comparable effect (56.25%). The neutron dose was compared at varying distances from the field edge. The neutron dose was higher in the order of AC(+ 11.96%p), MLC(+ 2.61%p), and no collimator at the 10 cm distance from field edge. For the dosimetric study, treatment plans for the nasal cavity, prostate, liver, lungs, and breasts were generated by the treatment planning system using the MC algorithm. Three treatment plans were developed for each of these five sites: line scanning without any collimation, line scanning with patient-specific ACs, and line scanning with MLCs. These plans were then compared dosimetrically, and gamma pass-rates were measured at various depths. These multifaceted comparisons showed that the use of an AC optimized the OAR sparing effect, with an MLC having similar effects, while maintaining the same target coverage and producing less neutron dose. All measurement results demonstrated a gamma pass-rate (2%, 2 mm) of over 90%, indicating the feasibility of implementing these techniques in actual clinical practice.

Group-III monochalcogenides, particularly gallium sulfide (GaS), have garnered attention for visible–UV range optoelectronic applications owing to their wide bandgap, which can reach approximately 3 eV. The interplay between group-III monochalcogenides and metal electrodes needs to be understood to optimize the device performance. In this study, we explored the Schottky barrier height between GaS deposited through atomic layer deposition and commonly employed Ti/Au electrodes through low-temperature current–voltage measurements. The GaS photodetector exhibited p-type transport characteristics with a mobility of 7.71 × 10^–1 cm² V⁻¹ s⁻¹ and a photoresponsivity of 547 A W⁻¹.

While spontaneous spin polarization is a desirable property in semiconductors, it has not been observed in pristine materials. A theoretical study suggested that the Au/Si(553) surface exhibits anti-ferromagnetic properties spontaneously. The Si(5 5 12) surface shares a similar atomic structure with the Au/Si(553) surface, particularly the presence of a stable honeycomb chain. The Si(5 5 12) surface exhibits four distinct surface structures: honeycomb chain, dimer, adatom, and tetramer. We find that while the pristine Si(5 5 12) shows no spin polarization, the doped Si(5 5 12) surface leads to spin splitting, primarily concentrated at the dangling bonds of the adatom and honeycomb chain. This spin splitting induces a transformation of the surface into a ferromagnetic state. Although the behaviors are rather different for the electron and hole doping, the surface magnetization roughly strengthens as the number of doped charges increases. These findings suggest that charge doping can be a viable approach to induce spin polarization in Si(5 5 12) surfaces, offering a potential route towards achieving this desired property in semiconductors.

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 motivation of geometry engineering with proton, deuteron, and helium-3 projectiles at relativistic heavy-ion collider (RHIC) is to investigate the relation between initial geometry and final momentum anisotropy, which is thought to be strong evidence of quark–gluon plasma. PHENIX Collaboration shows a hierarchy of elliptic and triangular flow in p/d/(^{3})He+Au collisions that follow a hierarchy of eccentricity described by the Monte Carlo Glauber model, whereas STAR Collaboration shows a different trend in the triangular flow results. For a complete understanding of the results, a detailed microscopic description, such as sub-nucleon geometry and area of energy deposition, becomes more important. A multiphase transport model (AMPT) can qualitatively describe the collective behavior with scatterings at partonic and hadronic stages. We utilize the AMPT to simulate small systems and investigate the relation between initial geometry and final momentum anisotropy with different geometry descriptions.

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.