Identification of Underground Artificial Cavities Based on the Bayesian Convolutional Neural Network.

The development of underground artificial cavities plays an important role in the exploitation of urban spatial resources. As the rapidly growing number of underground artificial cavities with different depths and scales increases, the detection and identification of underground artificial cavities has become a key issue in underground engineering studies. Geophysical techniques have been widely used for the construction, management, and maintenance of underground artificial cavities. In this study, we present two identification methods for underground artificial cavities. Apparent resistivity imaging is the most popular technique for quickly identifying underground artificial cavities, using the forward simulation results of a three-dimensional earth model and comparing these with the preset positions of artificial cavities, as demonstrated in the experiment. To further improve the efficiency of underground artificial cavity identification, we developed a fast recognition approach for underground artificial cavities based on the Bayesian convolutional neural network (BCNN). Compared to a traditional convolutional neural network, the performance of the BCNN method was greatly improved in terms of the classification accuracy and efficiency of identifying underground artificial cavities with apparent resistivity image datasets.

Mutagenesis of the di-leucine motif in the cytoplasmic tail of newcastle disease virus fusion protein modulates the viral fusion ability and pathogenesis.

BACKGROUND: Newcastle disease virus (NDV) is a highly infectious viral disease, which can affect chickens and many other kinds of birds. The main virulence factor of NDV, the fusion (F) protein, is located on the viral envelope and plays a major role in the virus' ability to penetrate cells and cause host cell fusion during infection. Multiple highly conserved tyrosine and di-leucine (LL) motifs in the cytoplasmic tail (CT) of the virus may contribute to F protein functionality in the viral life cycle. METHODS: To examine the contribution of the LL motif in the biosynthesis, transport, and function of the F protein, we constructed and rescued a NDV mutant strain, rSG10*-F/L537A, with an L537A mutation using a reverse genetic system. Subsequently, we compared the differences in the syncytium formation ability, pathogenicity, and replication levels of wild-type rSG10* and the mutated strain. RESULTS: Compared with rSG10*, rSG10*-F/L537A had attenuated syncytial formation and pathogenicity, caused by a viral budding defect. Further studies showed that the LL-motif mutation did not affect the replication, transcription, or translation of the virus genome but affected the expression of the F protein at the cell surface. CONCLUSIONS: We concluded that the LL motif in the NDV F CT affected the regulation of F protein expression at the cell surface, thus modulating the viral fusion ability and pathogenic phenotype.

Optimized fan-shaped chiral metamaterial as an ultrathin narrow-band circular polarizer at visible frequencies.

Chiral metamaterials have the great ability to manipulate the circular polarizations of light, which can be utilized to build ultrathin circular polarizers. Here we build a narrow-band circular polarizer at visible frequencies based on plasmonic fan-shaped chiral nanostructures. In order to achieve the best optical performance, we systematically investigate how different fabrication factors affect the chiral optical response of the fan-shaped chiral nanostructures, including incident angle of vapor depositions, nanostructure thickness, and post-deposition annealing. The optimized fan-shaped nanostructures show two narrow bands for different circular polarizations with the maximum extinction ratios 7.5 and 6.9 located at wavelength 687 nm and 774 nm, respectively.

Real-time in situ study of femtosecond-laser-induced periodic structures on metals by linear and nonlinear optics.

Femtosecond-laser surface structuring on metals is investigated in real time by both fundamental and second harmonic generation (SHG) signals. The onset of surface modification and its progress can be monitored by both the fundamental and SHG probes. However, the dynamics of femtosecond-laser-induced periodic surface structures (FLIPSSs) formation can only be revealed by SHG but not fundamental because of the higher sensitivity of SHG to structural geometry on metal. Our technique provides a simple and effective way to monitor the surface modification and FLIPSS formation thresholds and allows us to obtain the optimal FLIPSS for SHG enhancement.

Tuning the plasmonic properties of silver nanopatterns fabricated by shadow nanosphere lithography.

Regular silver (Ag) nanopatterns, from disconnected nanotriangles to well coupled triangular clusters of nanoparticles, were prepared by shadow nanosphere lithography at different incident angles θ from 0° to 20° with continuous azimuthal rotation. The resulting nanopatterns were consistent with predictions by numerical calculations and Monte Carlo simulations of adatoms with high diffusivity. The visible localized surface plasmon resonance of these nanopatterns was tuned by θ systematically due to the change in size, shape, and arrangement of Ag nanopatterns. These resonances were consistent with finite-difference time-domain simulations using realistic nanopatterns based upon scanning electron micrographs. Such a simple fabrication strategy can be used to optimize surface enhanced Raman scattering substrate fabrication, as well as other plasmonics based applications.

Circular dichroism based refractive index sensing using chiral metamaterials.

A new strategy to improve the sensing ability of localized surface plasmon resonance sensors is presented. By employing chiral plasmonic nanostructures, circularly polarized differential transmittance can show enhanced sensing performance over circularly polarized transmittance under certain conditions.

The fabrication of three-dimensional plasmonic chiral structures by dynamic shadowing growth.

As chiral metamaterials become increasingly more technologically relevant, scalable, yet proficient nanofabrication methods will be needed for their production. Dynamic shadowing growth (DSG) that takes advantage of the vapor shadowing effect during physical vapor deposition is a simple and powerful tool to produce chiral nanostructures. In this report we describe several new DSG strategies for the scalable production of chiral plasmonic thin films with significant optical activity in the visible and near-infrared wavelength region. Specifically, we demonstrate that by use of metal composite (Ti/Ag) and metal/dielectric composite materials (Ag/MgF2), nanoscale helices can be fabricated using DSG at room temperature. Additionally, we show how self-assembled colloidal monolayers of nanospheres can serve as effective templates for the production of a wide variety of highly chiral films. These films can be used to construct chiral metamaterial-based devices for future applications.

Tunable three-dimensional helically stacked plasmonic layers on nanosphere monolayers.

We report a simple and scalable method to fabricate helical chiral plasmonic nanostructures using glancing angle deposition on self-assembled nanosphere monolayers. By controlling the azimuthal rotation of substrates, Ag and SiO2 layers can be helically stacked in left-handed and right-handed fashions to form continuous helices. Finite-difference time-domain simulations confirm the experimental results that show that these plasmonic helices exhibit strong chiroptical responses in the visible to near-IR region, which can be tuned by changing the diameter of nanospheres. With such flexibility in the design, helically stacked plasmonic layers may act as tunable chiral metamaterials, as well as serve as different building blocks for chiral assemblies.

Hidden chirality in superficially racemic patchy silver films.

Chiral patchy particle films where morphological enantiomers exist in equal proportion are found to have significant circular dichroism. It is determined that the rotation direction during glancing angle deposition breaks the racemic symmetry, resulting in a distribution of material which enhances the chirality of one set of enantiomers relative to the other. Microscopic analysis and geometric chirality calculations reveal that the chirality of the bulk film results from incomplete cancellations of even stronger local chiralities.

Ag nanoparticle embedded TiO(2) composite nanorod arrays fabricated by oblique angle deposition: toward plasmonic photocatalysis.

Using a unique oblique angle co-deposition technique, well-aligned arrays of Ag nanoparticle embedded TiO2 composite nanorods have been fabricated with different concentrations of Ag. The structural, optical, and photocatalytic properties of the composite nanostructures are investigated using a variety of experimental techniques and compared with those of pure TiO2 nanorods fabricated similarly. Ag nanoparticles are formed in the composite nanorods, which increase the visible light absorbance due to localized surface plasmon resonance. The Ag concentrations and the annealing conditions are found to affect the size and the density of Ag nanoparticles and their optical properties. The Ag nanoparticle embedded TiO2 nanostructures exhibit enhanced photocatalytic activity compared to pure TiO2 under visible- or UV-light illumination. Ag plays different roles in assisting the photocatalysis with different light sources. Ag can be excited and can inject electrons to TiO2, working as an electron donor under visible light. While under UV illumination, Ag acts as an electron acceptor to trap the photogenerated electrons in TiO2. Due to the opposite electron transfer direction under UV and visible light, the presence of Ag may not result in a greater enhancement in the photocatalytic performance.

Porous three-dimensional nanorod arrays through selective chemical etching of nanocomposites.

Three-dimensional Cu-Si and Cu-SiO(2) nanorod arrays containing ~68 at% Cu have been fabricated by a glancing angle co-deposition technique. By selectively etching Cu in 0.05 M KCN methanol solution, porous nanorods with different shapes form, which are promising for applications in sensors, catalysts, and as medical capsules that are able to be loaded with functional materials.