We report a four-body calculation of associative ionization cross sections in S-wave collisions between a muonic hydrogen atom and an ordinary hydrogen atom, p (1s) + H(1s) . Because the energy released during the formation of the muonic molecular ion ( pp ) exceeds 100 eV, the associative ionization in this system is exothermic, producing pp and a free electron. We performed scattering calculations with two open channels for the spin-singlet and triplet states of two protons. At collision energies below 0.5 eV, the formation cross sections for the excited state of pp follow Wigner’s threshold law at collision energies below 0.5 eV. The calculated pp formation rate is consistent with, though slightly lower than, the experimental value measured in hydrogen gas [V. A. Andreev et al., Phys. Rev. C 91, 055502 (2015)].
Plasma-activated water (PAW) was generated using an atmospheric pressure plasma jet and investigated in terms of its physicochemical properties and storage stability. Optical emission spectroscopy indicated the presence of reactive species such as OH radicals and atomic oxygen, indicating oxygen-dominated plasma chemistry. Hydrogen peroxide increased to 240 mg/L, while nitrate and nitrite reached 100 mg/L and 11 mg/L, respectively, at 20 min of treatment. These changes were accompanied by a decrease in pH to 3.04, an increase in ORP to 510 mV, and an increase in conductivity from 15.4 to 28 mS·cm⁻1, indicating the formation of a highly oxidative liquid. During four weeks of storage, hydrogen peroxide and nitrite decreased, whereas nitrate remained relatively stable. In parallel, pH increased, while ORP and conductivity decreased, reflecting reduced reactivity. These results suggest that PAW is a dynamically evolving system, in which oxygen-containing plasma chemistry may contribute to the formation and long-term stability of reactive species.
Finite graphene nanoflakes occupy a unique position in the carbon allotrope landscape. Near equilibrium, these systems exhibit pronounced structural robustness, indicating that large-scale allotropic transformations require strongly non-equilibrium energy deposition. In this work, we investigate how unpassivated graphene edges act as chemically active gateways for collision-driven topological transformations in finite graphene systems. Using reactive molecular dynamics simulations, we model energetic collisions involving a C _60 fullerene projectile and a finite C _296 graphene nanoflake across a broad parameter space of collision energies, incidence angles, and edge orientations. The structural response is analysed through statistical transformation maps that quantify the probability of nanoflake bending, edge stitching, and the formation of nanotube-like structures. We identify a regime of collision energies and oblique incidence angles under which localised energy deposition at unpassivated edges promotes bond rearrangement, cooperative bending, and covalent stitching between opposing edges. Furthermore, we find that armchair-directed impacts align opposing zigzag edges and promote efficient edge-to-edge stitching over a broader parameter range. In contrast, zigzag-directed impacts are associated with a higher probability for atom ejection and bring opposing armchair edges into contact, which is less favourable for seam propagation, resulting in a narrower parameter window for nanotube-like structure formation. These results establish a non-equilibrium framework linking local edge chemistry and collision-induced energy deposition to topological evolution in finite graphene systems. The results demonstrate collision-driven self-organisation as a viable pathway for the emergence of tubular nanostructures without reliance on catalytic surfaces or sustained thermal annealing.
The fragmentation of uridine 5′-monophosphate (UMP) induced by MeV carbon cluster ions Cn+ (n = 1–4) was investigated using time-of-flight secondary-ion mass spectrometry. This process is directly correlated with three-dimensional ionization density rather than linear energy transfer (LET). By varying the cluster size at a fixed projectile velocity, the spatial proximity of ionization events was systematically controlled while maintaining comparable atomic velocities. A clear shift in fragmentation patterns was observed: the relative yield of base-derived fragments increased with cluster size, whereas contributions from the ribose- and phosphate-related fragments decreased. The magnitude of the linear electronic stopping power alone does not fully account for this trend. Comparison with monoatomic ions of comparable stopping power reveals a cluster-specific enhancement of base-related fragmentation. When the data are analyzed using a modified stopping parameter that incorporates geometrical ion-track overlap, consistent scaling behavior is observed across both monoatomic and cluster projectiles. These results indicate that molecular fragmentation is more closely correlated with the spatial concentration of deposited electronic energy rather than with one-dimensional energy loss alone. The findings suggest that controlled cluster irradiation provides a useful approach for probing molecular processes under spatially concentrated ionization conditions.
We present an experimental study of detuning-dependent properties of a laser-cooled cesium cloud in a magneto-optical trap. Fluorescence images are used to extract the cloud size, shot-to-shot width fluctuations, optical depth, density profiles, and spatial density fluctuation spectra as the trapping laser detuning is varied. Near resonance, the cloud exhibits larger spatial extent, increased width fluctuations, higher optical depth, and enhanced density fluctuation power, while larger detunings produce a more reproducible and spatially confined cloud. The measured density profiles are analyzed phenomenologically using a generalized Lane–Emden model with a polytropic equation of state, yielding detuning-dependent effective fit parameters in a weak interaction regime. Power spectrum and autocorrelation analyses reveal reproducible scale-dependent density correlations. The results provide a quantitative characterization of detuning-dependent radiative and collective effects in a cesium MOT and establish a basis for future measurements that can more directly test nonequilibrium transport and photon-mediated interaction models.
A neutral-beam injection scheme for magnetically trapping electrons and positrons is proposed. Pulsed lasers excite positronium (Ps) to long-lived Rydberg states that drift at speeds of |v⃗| ∼ 10^5 m s^-1 into the magnetic field of a levitated superconducting coil. The electric field experienced in the reference frame of the rapidly moving atoms is sufficient to ionize a significant portion of the loosely bound Ps. The released electrons and positrons are confined to the poloidal magnetic field lines that wrap around the coil. Rydberg positronium injection (RPI) does not perturb the confinement volume and ensures local charge symmetry. The technique provides equal, low temperatures for the electron and positron distributions, as well as smooth, inwardly peaked density profiles. The range of populated field lines depends on the Ps velocity distribution and the ionization threshold of the Rydberg state. Monte Carlo simulations are used to evaluate the e^+ efficiency of RPI for the APEX (A Positron–Electron eXperiment) levitated dipole.
We present a detailed theoretical investigation of the size and strain-dependent linear and nonlinear optical response of ZnxCd1−xSe/ZnSe disk-shaped quantum dots (QDs). The complex valence–band structure of QDs was computed using 4 × 4 k.p Luttinger Hamiltonian. The results reveal a strong sensitivity of the optical response to both strain and QD height. Increasing the compressive strain from 4.15 to 5.46
In this study, we propose a method for measuring the refractive index of materials in the sub-terahertz frequency range based on phase-shift analysis using a coherent continuous-wave radiation source and a matrix detector. The spatial distribution of the phase shift across the beam cross section was reconstructed from interference patterns obtained with a Mach–Zehnder interferometer. Refractive indices were determined for wedge-shaped and plane-parallel samples made of Teflon and polymeric glass sample.
Conventional multi-gap bunchers exhibit the problems of easy excitation of high-order modes and excessive axial size as the number of periods increases. Thus, this paper proposes a novel Ku-band coaxial transit-time oscillator with a double-gap buncher, aiming for compact design and high-efficiency performance in Ku-band high-power microwave sources. The double-gap buncher design can effectively suppress the excitation of high-order modes and ensure single-mode operation while greatly reducing the axial length of the buncher to achieve overall compactness. Furthermore, it combines the advantage of the low space-charge effect inherent in the coaxial structure to enhance the beam-wave interaction efficiency under a low guiding magnetic field. Finally, particle-in-cell simulation results demonstrate that under an acceleration voltage of 450 kV, a beam current of 7 kA, and a guiding magnetic field of 0.5 T, the TTO outputs an average power of 1.19 GW at 14.02 GHz, with a power conversion efficiency of 37.8
High-accuracy calculations of excitation energies and fine-structure splittings are reported for the 2s^22p^2(^3P)3p ^4D^∘ , ^4P^∘ and ^4S^∘ quartet bound states of neutral nitrogen. Extensive nonrelativistic configuration interaction (CI) calculations are performed using a combination of a priori selected CI and CI-by-parts (CIBP) techniques, enabling the systematic inclusion of electron correlation effects up to septuple excitation while keeping the effective CI dimensions computationally manageable. Near-full-CI convergence is achieved through careful control of CI space growth and basis set extrapolation. Relativistic corrections are evaluated within the framework of the Dirac–Coulomb–Breit Hamiltonian using relativistic CI calculations, which are added consistently to the nonrelativistic energies. The impact of the Breit interaction on excitation energies and fine-structure splittings is analyzed in detail. The calculated excitation energies are in excellent agreement with available experimental data, with residual deviations of only a few cm ^-1 . Fine-structure splittings are reproduced to better than 1 cm ^-1 , demonstrating the reliability of the combined correlation and relativistic treatment. The present results establish a robust and efficient computational framework for achieving spectroscopic accuracy in complex open-shell atomic systems. Schematic representation of the computational strategy combining large-scale nonrelativistic CI (up to septuple excitations) with relativistic CI corrections (including Breit interaction) to achieve spectroscopic accuracy for the excited quartet states of neutral nitrogen, with calculated excitation energies and fine structure splitting’s compared against NIST experimental data.
Traditional wire scanners for measuring low-intensity charged-particle beams face significant limitations due to X-ray background and technical challenges in signal detection. We propose a transverse-profile scanner based on optical-fiber technology, employing side-view detection of light yield from the fiber surface at 90^∘ with respect to the beam trajectory. The method uses an objective (Tamron 70–300 mm f/4.5–6.3 Di III RXD) and a CMOS camera (QHY533C) to capture the 2D light distribution along the fiber. In this work, we tested and compared the light yield of two fiber types: a 1 mm thick polymethyl methacrylate fiber and a 1 mm thick wavelength-shifting fiber. Tests were conducted at the TPU microtron with a 5.7 MeV electron beam (macro-pulse duration: 0.5 s, macro-pulse current: 360 A). Comparative measurements with a wire scanner demonstrate that the fiber scanner reliably detects the beam and provides a qualitative 2D image of the light distribution suitable for low-intensity beams. Systematic effects—including convolution with the fiber diameter, optical defocus, camera point-spread function, and light transport along the fiber—limit the quantitative accuracy of the extracted beam size. The results confirm the feasibility of the technique as a simple and fast diagnostic for commissioning and low-intensity operation. Future work will focus on calibration and correction of these systematic contributions to enable absolute beam-profile monitoring. Schematic of an optical-fiber scanner for transverse profile measurement of low-intensity charged-particle beams
Plasma treatment is a potent technique for altering surface properties of polymer without changing its bulk characteristics. In this study, polyvinyl chloride (PVC) and poly(methyl methacrylate) (PMMA) are treated using argon gas-based APPJ. The effect of plasma exposure times on the surface morphology and optical behavior was examined. Surface texture and roughness was measured by atomic force microscope (AFM), indicating the nanoetching effect and restructuring of surface using plasma. Surface degradation in both polymers is significantly evident from UV–Vis spectra. These findings were further verified by FT-IR analysis. Water contact angle measurements indicate a shift toward increased wettability of the surface as a function of surface plasma exposure time.
We study the influence of a semi-infinite confinement, attached to an oscillator-shaped quantum well on its dipole and quadrupole radiation properties. The effect of semi-infinite confinement is achieved thanks to the use of the position-dependent mass formalism. The time-independent Schrödinger equation describing the system is exactly solvable in the configuration representation, and the corresponding wave functions are expressed in terms of Laguerre polynomials. A remarkable property of the model is that its discrete energy spectrum coincides exactly with the linear spectrum of the non-relativistic harmonic oscillator. Additionally, such a confined quantum system preserves its exact solvability even in the presence of an applied homogeneous external field. This allows both dipole and quadrupole radiation characteristics to be calculated analytically despite the simultaneous presence of the modified confinement profile and the external perturbation. Analytical expressions for the dipole and quadrupole moment matrix elements are obtained in terms of the confinement parameter and the external field strength. We analyze the dependence of these matrix elements and the corresponding radiation intensities on both parameters. In particular, although the discrete energy spectrum remains unchanged, the confinement effect transforms transitions that are forbidden in the harmonic oscillator – namely Δ n=± 1 and Δ n=0 in dipole radiation and Δ n= ± 2 in quadrupole radiation–into allowed ones. In the presence of the external homogeneous field, the confinement effect further modifies these transitions by introducing an explicit dependence on the field strength. Finally, we derive limiting relations showing that the model reduces to the standard non-relativistic harmonic oscillator when the confinement parameter tends to infinity and the external homogeneous field vanishes.
This article analytically investigates long-wavelength transitions in a highly prolate ellipsoidal quantum dot containing a pair-interacting electron gas. Given the quantum dot’s specific geometry, the problem is initially considered within the adiabatic approximation. The interaction between electrons is assumed to be pairwise and one-dimensional (in axial direction). It is shown that for the slow subsystem describing the gas states along the elongated semiaxis of the ellipsoid, the multiparticle Schrödinger equation contains, on the one side, a parabolic constraint potential for each electron and, on the other side, a term describing the pairwise interaction energy between electrons. The interparticle interaction operator is considered within the framework of the exactly solvable Calogero model, which allows one to separate the center-of-mass motion from the relative motion, thereby demonstrating the realization of the generalized Kohn theorem under the action of long-wavelength radiation.
Metal-semiconductor hybrid nano-heterostructures have been under extensive study owing to their potential applications in optoelectronic devices, biosensing etc. In this study, glass/Ag/Cu2O layered thin film heterostructures with varying thickness of the top Cu2O layer were fabricated by reactive magnetron sputtering technique. While X-ray diffraction and Raman spectroscopy establish the formation of the aforesaid structure, detailed analysis of the surface morphology was performed by statistical analysis of atomic force microscopy images. The UV–visible absorption spectra of the samples reveal systematic increment in the absorbance with increasing thickness of the Cu2O layer. A significant enhancement in photoluminescence (PL) intensity of up to 400
The additive manufacturing of metal nanostructures using direct-write focused electron beam-induced deposition (FEBID) requires exploration and development of new metal-coordinated precursor complexes. In this study, we introduce (η2-fumaronitrile)(tetracarbonyl)ruthenium(0), a novel FEBID precursor designed using a mechanism-based approach in which the ligand set consists of neutral two-electron donor ligands weakly bound to the metal centre atom. Nanostructures were fabricated using this precursor via FEBID, and their elemental composition was determined through energy-dispersive X-ray spectroscopy. The resulting deposits consistently exhibited a metal content in the range of 8–12 at.
This study reports a four-body calculation of the radiative dissociation of positronium molecules ( Ps_2 ) in an excited state. The excited state of Ps_2 lies between the Ps ( n=1 ) + Ps ( n=1 ) and Ps ( n=1 ) + Ps ( n=2 ) thresholds and spontaneously dissociates into Ps ( n=1 ) + Ps ( n=1 ) through an electric dipole transition accompanied by photon emission. The energy spectrum and dissociation rates are calculated using a complex coordinate rotation method within the dipole approximation. The total radiative dissociation rate is 0.044 ns^-1 , which is one order of magnitude smaller than that of the electric dipole transition to the ground state of Ps_2 . The branching ratio of the radiative dissociation among the all spontaneous decay modes, including annihilation, has been determined to be 1.5
Single-photon emitters (SPEs) in two-dimensional materials are key resources for quantum technologies, but their efficiency is limited by radiation losses. Purcell-enhanced emission is studied by coupling strain-induced SPEs in monolayer WSe _2 to high-index GaP trimer nanostructures intentionally designed to support interference-induced quasi-bound states in the continuum (q-BIC) at the emission wavelength of WSe _2 SPEs. A comparative analysis between dimer and trimer configurations demonstrates that the q-BIC-assisted trimer effectively suppresses radiation losses, enhances the cavity quality factor, and produces remarkably brighter emission. These findings establish dielectric oligomer nanocavities supporting q-BIC-inspired interference resonances as a robust and scalable platform for deterministic single-photon sources in atomically thin semiconductors, advancing their integration into quantum photonic circuits. A schematic of GaP trimer nanostructure with a transferred monolayer of WSe₂ on top.
