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The luminescent mechanism of nano-sized materials with indirect bandgap and parity-forbidden transition has always been a critical issue in breaking through bottlenecks in traditional luminescent materials. The lack of understanding has resulted in great disputes regarding the origin of fluorescence in weak-transition nanocrystals (NCs). This paper proposes a new physical luminescence model, named as localized state-induced enhanced emission (LIEE), i.e., localized processes induced by size-limitation or partial doping, to explain the anomalous luminescence from non-luminescent state to luminescent state in various perovskite nanocrystals with indirect/direct bandgap or parity-forbidden transition. These findings provide a theoretical viewpoint to design efficient lead-free perovskite NCs and promote the development of fast optical transitions in luminescent materials.

We present a nitrogen-targeting-Proton-Carbon-Alpha-Therapy method, abbreviated as Proton-CAT, which partially converts protons into carbon-12 and $\alpha$ particles through nuclear reactions between protons and nitrogen-15. Monte Carlo simulations validated the effectiveness of the Proton-CAT, and the study specifically focused on the distribution of relative energy deposition. The results indicated that the presence of nitrogen-15 enhanced the maximum dose level of protons, resulting in more effective damage confined to tumor cells. Statistical analysis of secondary ions has shown that the Proton-CAT significantly increases the production efficiencies of carbon-12 and $\alpha$ particles. Furthermore, it has been revealed that elevating the nitrogen-15 concentration significantly boosts the dose of carbon and $\alpha$ particles within the tumor region. The present work would contribute to the future development of proton therapy., Comment: 5 pages, 4figures

In this work, we investigated the effect of ${\rm^{15}N(p,\alpha)^{12}C}$ reaction produced by the collision between proton and ammonia monohydrate on the kinetic energy release (KER) of water molecule fragmentation. After the occurrence of the nuclear reaction, it was found that the charge states $q$ and the flight speeds $v$ are the main factors affecting the KER of water molecule fragmentation. With the value of $q/v$ increases, the KER distribution gets wider and the peak position changes more pronounced. The energy gained by each fragment is related to the mass of the fragment and the distance of the fragment from the nuclear reaction. In this study, the fragments with smaller masses and the distances far away from the nuclear reaction get higher energies. The fragments of water molecules getting higher energy may induce other factors affecting the radiotherapy effect, which needs more detailed investigations in the future.

Coleman's theorem states that continuous internal symmetries cannot be spontaneously broken in two-dimensional quantum field theories (QFTs). In this work we consider surface (i.e. two-dimensional) defects in $d$-dimensional conformal field theories (CFTs) invariant under a continuous internal symmetry group $G$. We study under which conditions it is possible for a surface defect to break spontaneously a continuous internal symmetry. We find that spontaneous symmetry breaking (SSB) is impossible under reasonable assumptions on the defect Renormalization Group (RG) flow. Counterexamples are possible only for exotic RG flows, that do not terminate at a fixed-point. We discuss an example of this kind. We also illustrate our no-go result with an effective field theory analysis of generic defect RG flows. We find a generic weakly coupled defect universality class (with no SSB), where correlation functions decay logarithmically. Our analysis generalizes the recent discovery by Metlitski of the extraordinary-log boundary universality class in the $O(N)$ model., Comment: 37 pages+appendices, 3 figures, v2 several minor edits, v3 added app. B and minor edits, journal version

Silicon photoluminescence and lasing have been critical issues to breakthrough bottlenecks in the understanding of luminescence mechanisms. Unfortunately, long-standing disputes about the exciton recombination mechanism and fluorescence lifetime remain unresolved, especially about whether silicon nanocrystals (Si NCs) can realize fast direct-bandgap-like optical transitions. Here, using ground-state and excited-state density functional theory (DFT), we obtained intrinsic phonon-free optical transitions at sizes from Si22 to Si705, showing that very small Si NCs can realize a strong direct optical transition. Orbital labeling results show that this rapid transition does not come from the {\Gamma}-{\Gamma} -like transition, contrary to the conclusions from the effective mass approximation (EMA) and that {\Gamma}-X mixing leads to a quasi-direct bandgap. This anomalous transition is particularly intense with decreasing size (or enhancement of quantum confinement). By investigating electron and hole distributions generated in the optical transition, localized state-induced enhanced emission (LIEE) in Si NCs was proposed. Quantum confinement (QC) distorts the excited-state electron spatial distribution by localizing Bloch waves into the NC core, resulting in increased hole and electron overlap, thus inducing a fast optical process. This work resolves important debates and proposes LIEE to explain the anomalous luminescence--a phase transition from weak (or none) luminescent state to strong optical transition, which will aid attempts at realizing high-radiative-rate NCs materials and application-level Si lasers.