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Periodic structures structured as photonic crystals and optical lattices are fascinating for nonlinear waves engineering in the optics and ultracold atoms communities. Moiré photonic and optical lattices — two-dimensional twisted patterns lie somewhere in between perfect periodic structures and aperiodic ones — are a new emerging investigative tool for studying nonlinear localized waves of diverse types. Herein, a theory of two-dimensional spatial localization in nonlinear periodic systems with fractional-order diffraction (linear nonlocality) and moiré optical lattices is investigated. Specifically, the flat-band feature is well preserved in shallow moiré optical lattices which, interact with the defocusing nonlinearity of the media, can support fundamental gap solitons, bound states composed of several fundamental solitons, and topological states (gap vortices) with vortex charge s = 1 and 2, all populated inside the finite gaps of the linear Bloch-wave spectrum. Employing the linear-stability analysis and direct perturbed simulations, the stability and instability properties of all the localized gap modes are surveyed, highlighting a wide stability region within the first gap and a limited one (to the central part) for the third gap. The findings enable insightful studies of highly localized gap modes in linear nonlocality (fractional) physical systems with shallow moiré patterns that exhibit extremely flat bands. [ABSTRACT FROM AUTHOR]

To examine the pore structure characteristics of sandy silt in metro tunnel surrounding rock, the pore size distribution patterns and fractal dimension of sandy silt samples were determined through small-angle X-ray scattering (SAXS) experiments. This study also explored the relationship between the internal microscale pore structure of sandy silt and its macroscopic behavior. The results show that spherical pores within sandy silt predominantly exist in the forms of micropores and mesopores, with a concentrated distribution in the pore size range of 20–50 nm. Moreover, for scatterers with shapes like ellipsoids and disks, a smaller ratio of height to diameter or major axis to minor axis corresponds to a narrower range in observed pore diameter distribution, accompanied by a higher volume fraction. Meanwhile, the fractal dimensions for sandy silt samples B-1, B-2, and B-3 were 2.33, 2.33, and 2.38, respectively, aligning with the range of 2–3. The augmentation of fractal dimension corresponds to heightened surface irregularity or roughness, indicating a moderately smooth sandy silt surface. Additionally, the results show that the various deformation and strength characteristics possessed by the soil can be considered as a comprehensive reflection of the adjustment and evolution of its internal microscale pore structure elements. By utilizing the pore size distribution features and fractal dimension of the internal pore structure, a quantitative relationship between the internal pore structure of sandy silt and its macroscopic permeability or mechanical properties can be established. [ABSTRACT FROM AUTHOR]

In this research, optical absorption regulation of Ag nanodisc arrays in a monolayer MoS2 hybrid system is investigated using the FDTD technique. Ag nanodisc arrays are designed on monolayer MoS2 on SiO2/Si and Au/SiO2 substrates. For Ag/1L MoS2/SiO2/Si, two absorption peaks near 620 nm and 670 nm are showed, with different intensification amplitudes of absorption peaks and slight shifts in peak position changing diameters or spacing of Ag nanodiscs. When the diameter is 220 nm, the strongest absorption peak is displayed at 745 nm. When the spacing s is 300 nm, the absorption peak at 759 nm has the highest intensity. When the thickness of the SiO2 film increases from 90 to 280 nm and 300 nm, the intensity of the absorption peak near 620 nm increases by 1.7 times, and the peak blueshifts to 585 nm. In the band from 550 to 700 nm, the presence of the Ag nanodisc array significantly enhances the absorption of the film system, when the thickness of the SiO2 film is 300 nm, and the enhancement amplitude of the absorption peak near 620 nm reaches three times. For Ag/1L MoS2/Au/SiO2, when the diameter or spacing of the Ag nanodisc increases from 100 to 220 nm every 30 nm, the peak positions of 620 nm and 670 nm are changed. When the diameter of the Ag nanodisc is 100 nm and 220 nm, the normalized absorption rates at 686 nm and 707 nm are 0.95 and 0.96, respectively. When the spacing s is 200 nm and 400 nm, the normalized absorption rates at 562 nm and 686 nm are 0.94 and 0.96, respectively. By comparing the optical absorption with and without the Ag nanodisc array, the absorption of the monolayer MoS2 hybrid system is greatly enhanced. When the surrounding medium is changed from air to water, the absorption peaks of 641 nm and 686 nm become 587 nm and 775 nm, the distance between peak positions is enlarged, and the intensity is obviously weakened, which is due to the weakening of the surface plasmon effect of the Ag nanodisc array. [ABSTRACT FROM AUTHOR]

Highlights: A flexible tribotronic artificial synapse with bioinspired neurosensory behaviour was demonstrated, which establishes an active interaction mechanism with the environment. The device can well exhibit tuneable synaptic behaviours by changing the mechanical input modes, including excitatory postsynaptic current, paired-pulse facilitation, and the hierarchical memorial process. The device has excellent mechanical flexibility that can exhibit stable synaptic functions even under strain conditions with a bending radius of 20 mm after 1000 bending cycles. As key components of artificial afferent nervous systems, synaptic devices can mimic the physiological synaptic behaviors, which have attracted extensive attentions. Here, a flexible tribotronic artificial synapse (TAS) with bioinspired neurosensory behavior is developed. The triboelectric potential generated by the external contact electrification is used as the ion-gel-gate voltage of the organic thin film transistor, which can tune the carriers transport through the migration/accumulation of ions. The TAS successfully demonstrates a series of synaptic behaviors by external stimuli, such as excitatory postsynaptic current, paired-pulse facilitation, and the hierarchical memory process from sensory memory to short-term memory and long-term memory. Moreover, the synaptic behaviors remained stable under the strain condition with a bending radius of 20 mm, and the TAS still exhibits excellent durability after 1000 bending cycles. Finally, Pavlovian conditioning has been successfully mimicked by applying force and vibration as food and bell, respectively. This work demonstrates a bioinspired flexible artificial synapse that will help to facilitate the development of artificial afferent nervous systems, which is great significance to the practical application of artificial limbs, robotics, and bionics in future. [ABSTRACT FROM AUTHOR]

Electromagnetically induced optical (or photonic) lattices via atomic coherence in atomic ensembles have recently received great theoretical and experimental interest. We here conceive a way to generate electromagnetically induced moiré optical lattices — a twisted periodic pattern when two identical periodic patterns (lattices) are overlapped in a twisted angle (θ) — in a three-level coherent atomic gas working under electromagnetically induced transparency. We show that, changing the twisted angle and relative strength between the two constitutive sublattices, the moiré Bloch bands that are extremely flattened can always appear, resembling the typical flat-band and moiré physics found in other contexts. Dynamics of light propagation in the induced periodic structures demonstrating the unique linear localization and delocalization properties are also revealed. Our scheme can be implemented in a Rubidium atomic medium, where the predicted moiré optical lattices and flattened bands are naturally observable. [ABSTRACT FROM AUTHOR]

In this work, conical cavities with a fixed top diameter and varied bottom diameter have been utilized to improve the signal intensity, signal-to-noise ratio (SNR), and signal stability of laser-induced breakdown spectroscopy (LIBS). It is observed that the postponement of the maximum enhancement of spectral intensity and SNR occurs abnormally with decreasing the bottom diameter due to the energy dissipation from the plasma to the cavity walls. Optimization of the cavity size indicates that the conical cavity is superior to the widely-used cylindrical cavity in improving the performance of LIBS. It is also found that the emission enhancement in the conical cavity with larger bottom diameters is attributed to the increase in plasma temperature and electron number density, but the enhancement in the conical cavity with smaller bottom diameters is ascribed to the growth of electron number density. For the first time, the exact efficiencies of conical cavities suppressing the total number density fluctuation are acquired to evaluate the performance of improving signal stability through analysis of the signal uncertainty composition. [ABSTRACT FROM AUTHOR]

Carbon materials have become a research hotspot in many fields because of their unique properties. In this paper, carbon nanowires (CNWs) were constructed with the finite-difference time-domain (FDTD) technique, and the effects of different structural parameters on the optical absorption properties of CNWS arrays at 350–810 nm were investigated. The results show that different lengths, diameters and spacings of the nanowires lead to different absorption properties of the arrays. In addition to a sharp decrease in the absorption at high incidence or viewing angles, the arrays have strong absorption properties at other angles. However, the array absorption at high incidence or viewing angles can be enhanced to some extent by varying the lengths of the nanowires. The wavelength and polarization direction of the excitation light have little effect on the absorption properties of the arrays. It is very important to determine the corresponding structural parameters of CNWs with the strongest absorption for the fabrication of nanowire arrays and their applications in stealth technologies, nanolight-emitting devices, photoelectric sensors and photovoltaic cells. [ABSTRACT FROM AUTHOR]