Journal of the Korean Physical Society最新文献

Among cortical structures of various scales, macrocolumns are often proposed as the processing units that represent information or implement brain functions, according to the cell assembly theory. However, the precise role of macrocolumns in information processing remains unclear. In this study, we examine the firing properties of a cortical dynamics model to demonstrate how cortical blocks of a similar size to a macrocolumn serve as units that represent individual pieces of short-term memory information. Through analysis and simulations, we predict and observe the emergence of macrocolumn-sized activation clusters representing each piece of information in short-term memory. These clusters tend to remain in one place, much like a viscous substance, and spread out only minimally via short-range superficial connections. Instead, they can generate another activation that stores the same information in different locations via long-distance intercortical connections. These properties help to explain how the cerebrum can retain short-term memories for a long time—beyond the lifespan of activities maintained by recursive connections—and also why its capacity is severely limited as short-term memory.

The propagation of nonlinear dust-ion-acoustic waves in a three-component lunar dusty plasma consisting of warm positive ions, cold dust grains, and Maxwellian electrons is investigated. By employing the reductive perturbation technique, a Korteweg–de Vries (KdV) equation is derived to describe the weakly nonlinear evolution of the wave dynamics. The generalized Wronskian approach is then used to obtain positon, negaton, and positon-negaton interaction solutions, while the extended homogeneous balance method yields sinusoidal periodic, rational, kink-type, and explosive wave structures. The influences of the ion-to-dust mass ratio, ion-to-electron temperature ratio, electron-to-ion density ratio, and dust charge number on the phase velocity, nonlinearity coefficient, and nonlinear wave profiles are examined. The parametric analysis reveals that the amplitude and width of first-order negaton solitons increase with increasing ion-to-dust mass ratio and dust charge number, whereas enhanced electron-to-ion density ratio suppresses both characteristics. In contrast, higher ion-to-electron temperature ratio reduces the negaton amplitude. For second-order positons, growing ion-to-electron temperature and electron-to-ion density ratios lead to reductions in both wave amplitude and width. Furthermore, negaton solitons retain their essential characteristics after collisions with oscillatory singular structures, demonstrating their robustness during nonlinear interactions. The present findings contribute to the understanding of nonlinear dust-ion-acoustic structures and their interactions in lunar dusty plasma environments.

The body-centered tetragonal finite-difference time-domain (BCT-FDTD) method provides spatially collocated field components and reduced numerical-dispersion anisotropy relative to the standard Yee grid, but its original formulation assumes a uniform cell spacing that applies the same resolution everywhere in the domain. We extend BCT-FDTD to nonuniform grids by replacing the single per-axis spacing with cell-by-cell update coefficients (c_i = Delta t / Delta x_i), where (Delta x_i) is the local cell size at index i. Smooth variation between fine and coarse regions is guaranteed by an automatic geometric transition zone that keeps the ratio of adjacent cell sizes below 1.1 per step, while constraining each transition to span an integer number of cells so that the domain can be sized exactly. We systematically study the spurious reflection introduced at the grid-transition boundary as a function of the coarse-to-fine cell-size ratio (rho ) and the number of transition cells d, treating the two-point (x) and four-point (z) BCT stencils separately. A near-abrupt interface produces measurable backscattering, which the geometric grading suppresses monotonically with d to below the numerical-dispersion floor at the automatically chosen width. The four-point z-direction reflects 30–40 dB more strongly than the two-point x-direction at matched parameters, so the two require independent treatment; at the automatic grading both stay below (-60) dB for all (rho ) studied. The approach reduces the total cell count by a factor approaching (rho ^2) in the transverse plane relative to a uniform grid at the fine-region resolution, making BCT-FDTD practical for multiscale problems in nanophotonics and antenna design.

Constrained optimization problems are commonly addressed by applying simulated annealing (SA) to a composite energy consisting of a main objective term and a penalty term that discourages constraint violations. Although simple and widely used, this approach is highly sensitive to the choice of the penalty weight assigned to the constraint term. Inspired by gradient gating in machine learning, we introduce a gated SA scheme in which the contribution of the penalty term to the Metropolis acceptance test is considered only when its energy change has the same sign as that of the main objective. As a result, the penalty term can reinforce objective-improving moves but cannot drive the search against the primary objective. To ensure convergence under hard equality constraints, the acceptance criterion is referenced to an anchor, defined as the lowest-violation state encountered so far. Constraint-violating detours are accepted only if they eventually return to the anchor violation level, at which point the penalty contribution cancels exactly. This mechanism makes the dynamics intrinsically robust to the penalty weight, eliminating the need for instance-specific parameter tuning. For cardinality-constrained quadratic binary optimization, the proposed method achieves performance comparable to that of conventionally tuned SA at its optimal penalty weight and consistently outperforms standard SA across the entire range of penalty weights.

We investigate intra-chain exciton energy transfer (EET) in a conjugated polymer using a reduced three-level donor–acceptor model that separates vertical excitations from vibrationally relaxed states. Population dynamics are obtained with the hierarchical equations of motion (HEOM), enabling a non-Markovian treatment of system–bath (S–B) interactions. Case studies on Donor–Acceptor (D–A) pairs with small and large energy gaps reveal competition among coherent hopping, vibrational relaxation, and Förster resonance energy transfer (FRET). Varying the hopping and the S–B relaxation rate highlights roles of exciton transfer, thermal relaxation, and dipole-mediated coupling. The results show that energy gap, hopping, and relaxation jointly control intrachain EET.

Coherent elastic neutrino–nucleus scattering (CEvNS) provides a sensitive probe of neutrino interactions at low momentum transfer, but its experimental observation is strongly constrained by detector-related effects such as energy threshold, resolution, electronics noise, trigger response, and event-selection criteria. In this work, we perform a detector-response benchmark assessment of CEvNS nuclear recoil observability for alternative target nuclei, with particular emphasis on how a common detector-response model reshapes the measurable recoil spectra. Using Geant4-based simulations, CEvNS interactions are modeled for boron, magnesium, titanium, and zirconium targets under identical neutrino source, geometry, response, and selection assumptions. The generated nuclear recoil distributions are propagated through a parametric detector-response chain incorporating quenching, energy-resolution smearing, noise-induced fluctuations, measured-energy threshold selection, trigger response, and veto rejection. We present a systematic comparison of normalized true recoil-energy spectra, measured recoil-energy spectra after detector response, target-by-target true-to-measured spectral distortions, combined response-level acceptance, and threshold-dependent acceptance variations. The results show that detector-response effects significantly modify the observable CEvNS signal, particularly in the near-threshold region where the recoil population is most sensitive to smearing, noise, and threshold assumptions. The threshold-variation study demonstrates that lighter targets such as B and Mg retain comparatively stronger robustness against increasing measured-energy thresholds, whereas heavier targets, especially Zr, are more strongly affected because of their larger low-energy recoil concentration. Rather than providing absolute event-rate predictions or experiment-specific sensitivity projections, this study focuses on relative spectral behavior and response-level target comparison under controlled benchmark assumptions. The results highlight that CEvNS target evaluation cannot rely solely on weak-charge scaling or generator-level recoil spectra; detector threshold, resolution, noise, trigger response, and veto selection must also be considered. The presented framework provides a consistent methodology for comparing prospective CEvNS target materials at the detector-response level and can be extended in future work to include experiment-specific flux models, backgrounds, exposures, and detector technologies.

Positron emission tomography/computed tomography (PET/CT) is widely used to diagnose lung cancer. Accurate segmentation of lung cancer lesions in PET/CT images is critical for diagnosis and treatment planning. However, Poisson–Gaussian noise generated during image acquisition degrades image quality, particularly at lesion edges, reducing segmentation accuracy. The median-modified Wiener filter (MMWF) effectively reduces noise while preserving structural details; however, its performance highly depends on kernel size. This study aims to optimize the MMWF algorithm kernel size and evaluate its usefulness in reducing noise and improving cancer segmentation performance in lung cancer PET/CT images. We added Poisson–Gaussian noise with standard deviation of 0.001, 0.002, and 0.004 to PET/CT images to simulate low-, moderate-, and high-noise conditions, respectively, and compared the MMWF algorithm against conventional median and Wiener filters as baselines. The MMWF algorithm was optimized by increasing the kernel size from 3 (times) 3 to 13 (times) 13 in 2 (times) 2 increments. Quantitative evaluation results showed that the 9 (times) 9 kernel size achieved the highest segmentation and image quality performance across all evaluation metrics and noise levels. Statistical analysis using linear mixed-effects models confirmed that the optimized MMWF 9 (times) 9 demonstrated significantly superior performance compared with both baseline filters across all metrics (all p < 0.001). In conclusion, the optimized MMWF kernel size effectively reduces noise and improves segmentation accuracy in PET/CT images, highlighting the potential applicability of the MMWF algorithm in PET/CT-based lung cancer analysis.

Operating conditions for femtosecond pulse radiolysis were explored in the KAERI ultrafast electron diffraction (UED) beamline by adjusting the magnet settings without modifying the beamline layout. Three optimization scenarios were considered: maximum fluence at the sample position, minimum bunch duration under a fluence constraint, and maximum fluence under a bunch duration constraint. Under the maximum-fluence condition, the fluence increased with bunch charge, but the bunch duration also became longer because of stronger space-charge effects. For the 40 pC/mm² fluence constraint, the shortest bunch duration was achieved at 0.4 pC, reaching 38.7 fs at the sample position. With a bunch duration constraint of 50 fs, the maximum fluence was achieved at 0.8 pC, reaching 106.1 pC/mm². These results identify beam-dynamics conditions for delivering femtosecond electron bunches to an ultrathin liquid sheet sample and provide quantitative guidance for implementing pulse-radiolysis experiments in the present beamline.

We demonstrate a high-energy, spectrally combined diode-pumped long-cavity Ti:sapphire femtosecond laser designed for high-energy pulse generation and stable ultrafast operation. To overcome the pulse energy limitations of standard high-repetition-rate oscillators, a Herriott-type multipass cell was employed to extend the cavity length, achieving a reduced repetition rate of 25.5 MHz. The laser is pumped by three spectrally combined visible laser diodes operating at 465, 490, and 520 nm, providing a total pump power of 8 W. This multi-wavelength pumping configuration was carefully optimized to match the absorption profile of the Ti:sapphire gain medium while minimizing residual absorption losses at shorter wavelengths. The laser delivers 134-fs, 12-nJ pulses at a total pump power of 8 W, corresponding to an optical-to-optical efficiency of 3.8%. Stable mode-locking is maintained using a semiconductor saturable absorber mirror with a 0.8% modulation depth, resulting in a low long-term power fluctuation of 0.65% root mean square over 48 hours. Furthermore, a quantitative relative intensity noise analysis was performed to correlate the noise characteristics of individual pump diodes with the mode-locked output. The measured integrated relative intensity noise of 0.0537% suggests that the intrinsic gain-filtering effect of the Ti:sapphire medium effectively suppresses high-frequency pump-induced fluctuations. These results provide an efficient and scalable framework for developing high-energy diode-pumped ultrafast light sources.

A systematic first-principles investigation of the structural, electronic, and optical properties of tellurium-doped zinc oxide ZnTeₓO_1-x (x = 0, 1, 2, 3, 4, 5, and 100%) is presented. All calculations were carried out using the CASTEP plane-wave pseudopotential code under both the Local Density Approximation (LDA/CA-PZ) and the Generalized Gradient Approximation (GGA/PBE). Norm-conserving pseudopotentials were employed together with a plane-wave cutoff of 750 eV, and Brillouin-zone sampling was performed on a 4 × 4 × 4 Monkhorst–Pack mesh. Te doping was modeled using the virtual crystal approximation (VCA), which allows low and fractional Te concentrations to be treated directly. Equilibrium geometries were obtained with the BFGS algorithm, and equation-of-state parameters were extracted by fitting total energy–volume data to the Murnaghan equation. Both functionals show that lattice constant and unit cell volume expand monotonically with Te content, from a₀ = 3.287 Å (LDA) for pure ZnO to 4.304 Å for ZnTe, while the bulk modulus falls from 220.6 GPa to 42.6 GPa (LDA), reflecting the progressive replacement of stiff Zn–O bonds by softer Zn–Te bonds. The electronic band gap decreases rapidly from 0.561 eV (LDA) at x = 0 to zero at x ≥ 3%, suggesting a possible composition-driven semiconductor-to-metal transition within the LDA/GGA framework, driven by Te 5p–O 2p hybridization near the valence band maximum. This predicted gap closure should be interpreted with caution because standard LDA and GGA functionals underestimate band gaps. At full substitution (ZnTe), the gap re-opens at 1.498 eV (LDA). Optical spectra, including absorption coefficient, reflectivity, refractive index, extinction coefficient, and complex dielectric function, computed within the independent-particle Kubo–Greenwood formalism, confirm a strong ultraviolet activity in ZnO and reveal a systematic red shift in the absorption edge and significant modification in the dielectric response upon Te incorporation. The enhanced visible-light absorption indicates that Te doping can improve the optical response of ZnO for potential photovoltaic, photocatalytic, and optoelectronic applications.