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This paper presents an automated and effective method for detecting 3D edges and tracing feature lines from 3D-point clouds. This method is named Analysis of Geometric Properties of Neighborhoods (AGPN), and it includes two main steps: edge detection and feature line tracing. In the edge detection step, AGPN analyzes geometric properties of each query point’s neighborhood, and then combines RANdom SAmple Consensus (RANSAC) and angular gap metric to detect edges. In the feature line tracing step, feature lines are traced by a hybrid method based on region growing and model fitting in the detected edges. Our approach is experimentally validated on complex man-made objects and large-scale urban scenes with millions of points. Comparative studies with state-of-the-art methods demonstrate that our method obtains a promising, reliable, and high performance in detecting edges and tracing feature lines in 3D-point clouds. Moreover, AGPN is insensitive to the point density of the input data.

In this paper, we experimentally investigated the excitation of spoof surface plasmon polaritons (SSPPs) supported by a 1D subwavelength grating with a rectangular profile in the terahertz (THz) frequency range. Using the attenuated total reflection technique and the THz radiation of the Novosibirsk free electron laser, we carried out detailed studies of both angular and gap spectra at several wavelengths. A shallow grating supporting a fundamental mode was fabricated by means of multibeam X-ray lithography and used as a test sample. The results indicated that we achieved 1-THz tunability of resonance in the frequency range from 1.51 to 2.54 THz on a single grating, which cannot be obtained with active tunable metamaterials. The Q factors of the resonances in the angular spectra were within the range of 19.4–37.6, while the resonances of the gap spectra had a Q factor lying within the 1.17–2.03 range. The gap adjustment capability of the setup shown in the work has great potential in modulation of the absorption efficiency, whereas the angular tuning and recording data from each point of the grating will enable real-time monitoring of changes in the surrounding medium. All of this is highly important for enhanced terahertz real-time absorption spectroscopy and imaging.

Exotic physics could emerge from interplay between geometry and correlation. In fractional quantum Hall (FQH) states 1 , novel collective excitations called chiral graviton modes (CGMs) are proposed as quanta of fluctuations of an internal quantum metric under a quantum geometry description 2 – 5 . Such modes are condensed-matter analogues of gravitons that are hypothetical spin-2 bosons. They are characterized by polarized states with chirality 6 – 8 of +2 or −2, and energy gaps coinciding with the fundamental neutral collective excitations (namely, magnetorotons 9 , 10 ) in the long-wavelength limit. However, CGMs remain experimentally inaccessible. Here we observe chiral spin-2 long-wavelength magnetorotons using inelastic scattering of circularly polarized lights, providing strong evidence for CGMs in FQH liquids. At filling factor v  = 1/3, a gapped mode identified as the long-wavelength magnetoroton emerges under a specific polarization scheme corresponding to angular momentum S  = −2, which persists at extremely long wavelength. Remarkably, the mode chirality remains −2 at v  = 2/5 but becomes the opposite at v  = 2/3 and 3/5. The modes have characteristic energies and sharp peaks with marked temperature and filling-factor dependence, corroborating the assignment of long-wavelength magnetorotons. The observations capture the essentials of CGMs and support the FQH geometrical description, paving the way to unveil rich physics of quantum metric effects in topological correlated systems. Through inelastic light scattering chiral spin-2 long-wavelength magnetorotons are observed, revealing chiral graviton modes in fractional quantum Hall states and aiding in understanding the quantum metric impacts in topological correlated systems.

Previous studies on the propagation direction of valley topological edge states mainly focus on the matching between orbital angular momentum of the excitation source and specific pseudo-spin state of valley edge mode at certain frequency that falls in the bandgap of the topologically distinct bulk components. In this work, we propose topological photonic crystals (PCs) hosting two topological protected bandgaps. It is shown that by constructing the interface between different PC structures with distinct topological phase, edge states can be engineered inside these two bandgaps, which provides a convenient way to achieve flexible wave routing. Particularly, we study three types of meta-structures consisting of these PCs in which the valley edge states routing path highly depends on the operating frequency and inputting port of the excitation source. Our study provides an alternative way in designing topological devices such as wave splitters and frequency division devices.

The goal of this study was to investigate the structure and optical properties of the prepared PVC/NiO nanocomposites. The samples were characterized via XRD, TEM, SEM, and UV–Vis spectrophotometer experimental measurements. The partial crystal structure of PVC/NiO nanocomposites and cubic structure of NiO nanoparticles were explored by X-ray diffraction. SEM exhibited the good distribution of the nanoparticles in PVC films. Linear optical parameters: refractive index and normalized absorption, increased whenever transmission and reflection reduced by adding NiO nanoparticles. Direct and indirect optical band gaps were obtained from Tauc’s formula, and it was found that both direct and indirect optical band gaps decrease as more NiO nanoparticles added. The direct optical band gap decreases from 5.20 to 5.15 eV. The optical conductivity increased by increasing the content of NiO nanoparticles. The dispersion parameters: oscillator energy E 0 , dispersion energy E d , plasma angular frequency w p , optical momentum of dispersion M - 1 and M - 3 , and static refractive index, were calculated by using Wemple and DiDominco model. The nonlinear optical susceptibility x ( 3 ) and nonlinear refractive index n 2 were evaluated from the linear optical parameters using semiempirical relation. The increasing in nonlinear parameters x ( 3 ) and n 2 suggest the use of PVC/NiO nanocomposites for nonlinear optical applications.

A bstract We investigate the scattering of electromagnetic and gravitational waves off a Reissner-Nordström black hole in the low-temperature regime where the near-horizon throat experiences large quantum fluctuations. We find that the black hole is transparent to electromagnetic and gravitational radiation of fixed helicity below a certain frequency threshold. This phenomenon arises because the angular momentum of the black hole is quantized, creating an energy gap between the spinless black hole state and the first excited spinning states. Radiation with angular momentum — such as photons, gravitons, and partial waves of a massless scalar field, which we also study — must supply enough energy to bridge this gap to be absorbed. Below this threshold, no absorption can occur, rendering the black hole transparent. For frequencies above the gap, the scarcity of black hole states continues to suppress the absorption cross-section relative to semiclassical predictions, making the black hole translucent rather than completely transparent. Notably, electromagnetic absorption is significantly stronger than gravitational absorption, beyond what differences in spin alone would suggest.

A bstract We study the properties of the transition probability for a circularly accelerated detector that interacts with the massless scalar fields in the presence of a reflecting boundary. As the trajectory radius increases, the transition probability may exhibit some peaks under specific conditions, which can lead to the possibility of the identical result for different trajectory radius with the same acceleration and energy gap. These behaviors can be characterized by certain critical values. Furthermore, we analyze the entanglement harvesting phenomenon for two circularly accelerated detectors with a boundary. We consider that the two detectors are rotating around a common axis with the same acceleration, trajectory radius and angular velocity. When the detectors are close to the boundary, there may exist two peaks in entanglement harvesting. Interestingly, as trajectory radius increases, entanglement harvesting in some situations first decreases to zero, then remains zero, and finally increases to a stable value. Our results show that the features observed properties of the detectors are closely related to the vacuum fluctuations of the field and states of the detectors. Under appropriate conditions, circular motion can be used to simulate the results of uniform acceleration.

When a paramagnetic molecule is placed on a superconducting surface the lifetime of its spin excitations increases dramatically. This effect, caused by the depletion of the electronic states within the energy gap at the Fermi level, could find application in coherent spin manipulation. The latest concepts for quantum computing and data storage rely on the addressing and manipulation of single spins. A limitation for single atoms or molecules in contact with a metal surface is the short lifetime of excited spin states, typically picoseconds, due to the exchange of energy and angular momentum with the itinerant electrons of the substrate 1 , 2 , 3 , 4 . Here we show that paramagnetic molecules on a superconducting substrate exhibit excited spin states with a lifetime of τ ≈10 ns. We ascribe this increase in lifetime by orders of magnitude to the depletion of electronic states around the Fermi level in the superconductor. This prohibits pathways of energy relaxation into the substrate and allows the magnetic molecule to be electrically pumped into higher spin states, making superconducting substrates prime candidates for spin manipulation. We further show that the proximity of the scanning tunnelling microscope tip modifies the magnetic anisotropy.

ZnPSe₃ was identified as a two-dimensional material wherein valley and spin can be optically controlled in technologically relevant timescales. We report an optical characterization of ZnPSe₃ crystals that show indirect band-gap characteristics in combination with unusually strong photoluminescence. We found evidence of interband recombination from photoexcited electron–hole states with lifetimes in a microsecond timescale. Through a comparative analysis of photoluminescence and photoluminescence excitation spectra, we reconstructed the electronic band scheme relevant to fundamental processes of light absorption, carrier relaxation, and radiative recombination through interband pathways and annihilation of defect-bound excitons. The investigation of the radiative processes in the presence of amagnetic field revealed spin splitting of electronic states contributing to the ground excitonic states. Consequently, the magnetic field induces an imbalance in the number of excitons with the opposite angular momentum according to the thermal equilibrium as seen in the photoluminescence decay profiles resolved by circular polarization.

Most micro-electromechanical systems (MEMS) gyroscopes use capacitive detection to sense displacement from angular velocity, but parasitic capacitance and electromagnetic interference limit precision. Micro-opto-electro-mechanical systems (MOEMS) gyroscopes replace capacitive readout with optical detection, improving sensitivity and interference resistance, yet integrating optical structures with diverse motion modes remains challenging. We propose a high-sensitivity MOEMS y-axis gyroscope based on a double-layer two-dimensional photonic crystal array (2L2DPCA). One photonic layer is fixed to the substrate and the second is attached to a movable sensing mass, which enhances light confinement and reduces optical energy loss. A dual-decoupled beam design isolates nonplanar motion and suppresses cross-coupling in the x and y axes. Simulations show excellent in-plane uniformity and coupling-error suppression. Mechanical sensitivity reaches 57.82 nm/(°/s); overall output sensitivity after optoelectronic conversion is ≈31.24 mV/(°/s). Angular random walk (ARW) is 3.77×10⁻⁵ °/h1/2 for coupling gaps d≈0.1-0.2μm. Experimental results validate rotational response and indicate real-time performance potential in engineering and aerospace environments. The proposed device combines high sensitivity, reduced noise, and robust anti-interference characteristics, improving measurement accuracy and dynamic range for compact navigation and precision sensing applications.