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With the continuous development of artificial intelligence technology, image semantic segmentation has increasingly become the focus of computer vision and artificial intelligence algorithms. Image semantic segmentation technology has been applied in remote sensing satellite images, agricultural products production, medical diagnosis and treatment and other fields, and these fields need very accurate and effective semantic segmentation technology. This paper summarizes the common semantic segmentation techniques, introduces the main algorithms of image semantic segmentation techniques, mainly explains the image semantic segmentation techniques based on traditional machine learning and image semantic segmentation techniques based on deep learning, expounds the structure of each method, summarizes the performance and effect of each method, and finally expounds our views on the future development direction and challenges of semantic segmentation.

A series of environmentally nontoxic near-infrared reflective pigments of BiVO4 coated mica-titanium oxide were synthesized. The pigments were characterized by XRD, FE-SEM, UV–vis-NIR spectrophotometer and CIE L∗ a∗ b∗ color scales. The results illustrated that the BiVO4 particles with a size of ∼500 nm were firmly adhered to mica-titanium oxide substrate. Additionally, the composite pigments change the color from white to bright yellow with the increase of the BiVO4 loadings. All the pigments had higher NIR reflectance than conventional yellow pigment (≥70.0%). In the simulated experiment, the temperature difference of the inner surface temperature of coatings and the interior air temperature of boxes reached 4.5 °C and 2.3 °C, respectively, indicating that the good thermal insulation performance of the sample coating (30% BiVO4) could be used as building roof material to reduce the heat buildup and decrease the indoor temperature. Furthermore, we also evaluated aging resistance of the pigments. In conclusion, BiVO4 coated mica-titanium oxide composite pigments have great potential in serving as cool materials for building coatings and they also meet energy-saving and environmentally friendly requirements.

A series of novel nontoxic near-infrared (NIR) reflective pigments based on Al-doped BiFeO3 coated mica-titania were synthesized by precipitation combined with sol-gel method. The pigments of the formula BiFe1−xAlxO3/mica-titania (x = 0, 0.1, 0.2, 0.3, 0.4) were characterized by XRD, FE-SEM, TG-DTA, UV–vis–NIR spectrophotometer and CIE L* a* b* color scales. The results illustrate that the BiFeO3 nanoparticles are coated on the surface of mica-titania uniformly, and the doped BiFe1−xAlxO3/mica-titania is similar to BiFeO3/mica-titania composite in morphology. Furthermore, the absorption edge of composite pigments shift to shorter wavelength (533–495 nm) can be attributed to O2p-Fe3d charge transfer transitions and change the color of the pigments from brown to orange. Additionally, the NIR solar reflectance of the powdered pigments and pigmented coatings were measured. The results reveal that with the increase of progressive doping of Al3+ for Fe3+, the NIR solar reflectance of the pigments increase gradually and exhibit higher NIR solar reflectance (R* ≥ 47.8%) than the conventional pigment of similar color. Moreover, we also evaluated the thermal and chemical stability of the pigments. In conclusion, the pigments have the potential to be applied as “cool pigments”.

The scattering spectra and intensity of gold nanorods placed at varied distances above gold films have been simulated and measured under various conditions, demonstrating that scattering characteristics of the nanorod-film system are highly dependent on illumination conditions. Studying the surrounding electric fields of nanorods reveals that the illumination-dependent properties of the system are induced by the interference in the nanorod-film system. Both simulations and experiments show that optimising the nanorod-film distance can greatly enhance scattering magnitudes up to ~20 times for certain illumination conditions. We propose an application of the studied system in facilitating photo-thermal conversion.

The plasmonic resonances in individual gold nanorods nanoscopically coupled to a gold film with different gap spacing have been experimentally and theoretically investigated. The spectral widths, wavelengths, and optical polarizabilities of the maxima in measured single-nanoparticle scattering spectra are significantly modified as the gap distance changes in the sub-20 nm domain. Comparing the experimental data with numerical simulations reveals that these modifications arise from the complex hybridization of several dipolar and multipolar plasmon modes that are strongly localized at the gap. These plasmon gap modes have distinct resonant and spatial characteristics as a result of near-field interaction between the elongated nanorods and the gold film. Additionally, the excitation of these gap modes is highly dependent on the gap spacing. Finally, we also discuss influences of these plasmonic modes on absorption properties of the system and propose a potential application of the studied structures in faci...

Nanostructures with various configurations have been extensively used to engineer the emission properties of embedded fluorophores, but lack the flexibility to dynamically control fluorescence. Here we report a thin-film cavity system, comprising a quarter wavelength thick dye-doped dielectric coating on a reflecting surface, in which the fluorescence enhancement and directionality can be significantly modified by altering the illumination angle. The configuration of the cavity yields absorption properties that are highly dependent on illumination angles, due to the coupling between molecular absorption and Fabry-Perot resonances. Therefore the fluorescence intensity relating to the angle-dependent absorbing efficiency varies with illumination angles. In addition, as a result of synergy between intrinsic absorption of the reflecting surface, Fabry-Perot and surface-plasmon-polariton resonances and illumination-angle dependent excitation efficiencies for differently located molecules, the global emission intensity, including emission from dyes at all locations, can be directionally redistributed by altering the illumination angle.

Plasmonic cavities can be used to control the atom-photon coupling process at the nanoscale, since they provide an ultrahigh density of optical states in an exceptionally small mode volume. Here we demonstrate strong coupling between molecular excitons and plasmonic resonances (so-called plexcitonic coupling) in a film-coupled nanocube cavity, which can induce profound and significant spectral and spatial modifications to the plasmonic gap modes. Within the spectral span of a single gap mode in the nanocube-film cavity with a 3 nm wide gap, the introduction of narrow-band J-aggregate dye molecules not only enables an anticrossing behavior in the spectral response but also splits the single spatial mode into two distinct modes that are easily identified by their far-field scattering profiles. Simulation results confirm the experimental findings, and the sensitivity of the plexcitonic coupling is explored using digital control of the gap spacing. Our work opens up a new perspective to study the strong coupling process, greatly extending the functionality of nanophotonic systems, with the potential to be applied in cavity quantum electrodynamic systems.

Summary Background Predictors of quantitative evaluation of hepatic steatosis and liver fat content (LFC) using clinical and laboratory variables available in the general practice in the obese children are poorly identified. Objective To build predictive models of hepatic steatosis and LFC in obese children based on biochemical parameters and anthropometry. Methods Hepatic steatosis and LFC were determined using proton magnetic resonance spectroscopy in 171 obese children aged 5.5–18.0 years. Routine clinical and laboratory parameters were also measured in all subjects. Group analysis, univariable correlation analysis, and multivariate logistic and linear regression analysis were used to develop a liver fat score to identify hepatic steatosis and a liver fat equation to predict LFC in each subject. Results The predictive model of hepatic steatosis in our participants based on waist circumference and alanine aminotransferase had an area under the receiver operating characteristic curve of 0.959 (95% confidence interval: 0.927–0.990). The optimal cut-off value of 0.525 for determining hepatic steatosis had sensitivity of 93% and specificity of 90%. A liver fat equation was also developed based on the same parameters of hepatic steatosis liver fat score, which would be used to calculate the LFC in each individual. Conclusions The liver fat score and liver fat equation, consisting of routinely available variables, may help paediatricians to accurately determine hepatic steatosis and LFC in clinical practice, but external validation is needed before it can be employed for this purpose.

Surface plasmon polaritons (SPPs) propagating at metal nanostructures play an important role in breaking the diffraction limit. Chemically synthesized single-crystalline metal nanoplates with atomically flat surfaces provide favorable features compared with traditional polycrystalline metal films. The excitation and propagation of leaky SPPs on micrometer sized (10–20 μm) and thin (30 nm) gold nanoplates are investigated utilizing leakage radiation microscopy. By varying polarization and excitation positions of incident light on apexes of nanoplates, wave-vector (including propagation constant and propagation direction) distributions of leaky SPPs in Fourier planes can be controlled, indicating tunable SPP propagation. These results hold promise for potential development of chemically synthesized single-crystalline metal nanoplates as plasmonic platforms in future applications.

Metasurfaces, which consist of resonant metamaterial elements in the form of two-dimensional thin planar structures, retain great capabilities in manipulating electromagnetic wave and potential applications in modifying interaction with fluorescent molecules. The metasurfaces with magnetic responses are favorable to weakening fluorescence quenching while less investigated in controlling fluorescence. In this paper, we demonstrate control over fluorescence emission by engineering the magnetic and electric modes in plasmonic metasurfaces consisting of 45-nm-thick gold split-ring-resonators (SRRs). The fluorescence emission exhibits an enhancement factor of ∼18 and is predominantly x-polarized with assistance of the magnetic mode excited by oblique incidence with an x-polarized electric field. The magnetic and electric modes excited by oblique incidence with a y-polarized electric field contribute to the rotation of emission polarization with respect to the incident polarization. The results demonstrate manipulating the interaction of fluorescent emitters with different resonant modes of the SRR-based metasurface at the nanoscale by the polarization of incident light, providing potential applications of metasurfaces in a wide variety of areas, including optical nanosources, fluorescence spectroscopy and compact biosensors.

A non-complicated, controllable method of metallic nanoparticle fabrication at low operating light power is proposed. The method is based on laser-induced forward transfer, using a metamaterial absorber as the donor to significantly enhance the photothermal effect and reduce the operating light fluence to 35 mJ/cm(2), which is much lower than that in previous works. A large number of metallic nanoparticles can be transferred by one shot of focused nanosecond laser pulses. Transferred nanoparticles exhibit good size uniformity and the sizes are controllable. The optical properties of transferred particles are characterized by dark-field spectroscopy and the experimental results agree with the simulation results.

We review here our recent studies on plasmonic enhanced photothermal effects in metallic nanostructure, and the applications of such effects. When light is shined on a prefect metamaterial absorber patterned with e-beam lithography, the gold nanoparticles (NPs) forming the absorber can be either transformed to nano-spherical-domes, or to truncated-octahedral shaped or multi-twined nanocrystals with large crystal grain sizes and flat boundary facets. The evolution of morphology and crystallinity of the gold NPs can be also observed. Evidences clearly show that the surface melting and the coalescence mechanism play a key role on nanocrystals formation. These melted gold nanospheres can even be transferred to another substrate, on which the transferred NPs exhibit excellent size uniformity. The strong photothermal effects can also be utilized to tune silicon photonics waveguides and resonators. It is shown that all-optical photothermal switching of Mach-Zehnder interferometers (MZI), silicon disk resonators, and silicon ring resonators is possible with the help of plasmonic nanoheaters. The switching response time and power consumption are all at reasonably low level.

We experimentally demonstrate the strongly enhanced photoluminescence of the fluorescent molecules on the metamaterial mirror. The matematerial mirror can optimize the reflection phase to provide a large electric field for the 20-nm-thick active layer. Compared with the smooth gold plate, the experimental result shows a nearly 45 times enhancement.

Au nanoparticles show large third-order nonlinear effect and ultra-fast response. Here a high nonlinear aggregate film based on self-assembled gold nanoparticles is reported and its third-order nonlinear refractive index coefficient is measured by Z-scan experiment. The third-order nonlinear refractive index coefficient of the Au nanoparticle aggregate film (γ1 = 9.2 × 10−9 cm2/W) is found to be larger than that of an 8-nm-thick sputtered Au film (γ2 = 6.5 × 10−9 cm2/W). This large nonlinear effect can be attributed to the strong field enhancement due to localized plasmon resonances between Au nanoparticles. The result shows that the self-assembled Au nanoparticle aggregate film could be a promising candidate as a third-order nonlinear optical material.

An ultra-narrow band absorber consisting of continuous silver and alumina films is investigated. Owing to Fabry–Perot resonance and silver's inherent loss, an ultra-narrow spectral range of light can be entirely trapped in the structure. By varying thicknesses of metallic and dielectric films, absorption peak shifts in visible and near-infrared regions. When two such metal-insulator-metal stacks are cascaded, experimental results show that an ultra-narrow absorption bandwidth of 7 nm is achieved, though theoretical results give that of 2 nm. Features of high-efficiency and ultra-narrow band absorption have huge potential in optical filtering, thermal emitter design, etc.

In this paper, we experimentally demonstrate enhanced optical transmission through a seamless gold film based on the grating-insulator-metal (GIM) architecture. The transmittance of this GIM structure reaches 40% at 930 nm, showing 3.7 dB and 9.1 dB increase compared with a bare gold film and a continuous metal-insulator-metal stack, respectively. The enhanced transmission is polarization-sensitive and robust for oblique incidence. With tunable transmission peaks, such a device exhibits great potential for applications in optical filtering, polarization detecting and further integration in optoelectronics system.

Turning the surfaces of noble metals (metasurfaces) into black (highly absorptive) surfaces can be potentially applied in thermophotovoltaics, sensing, tailoring thermal emissivity, etc. Here we demonstrate an extremely broadband absorber for the 900-1600 nm wavelength range with robust high absorption efficiency. The inexpensive droplet evaporation method is implemented to create patterns of nanoparticles dispersed on a gold film spaced by a thin dielectric layer. The diversity of the complicated random stacking of the chemically synthesized gold nanorods is the major factor for the broad absorption band. Such a metamaterial absorber may pave the way for cost-effective manufacture of large-area black metasurfaces.