Reflective low-sideband plasmonic structural colors

It is demonstrated experimentally that an aluminum (Al) nanowire grating structure on silicon substrates can produce low-side-band monochromatic peak when it reflects colored light in the transverse magnetic (TM) mode. The central wavelength of the reflection is shown to be sensitive to the incident angle, which leads to significant color shifts. Formation of the monochromatic peak is attributed to the surface plasmon resonance on the interface between Al and air, together with remarkable diffraction at shorter wavelengths and strong Fabry-Perot (F-P) resonance absorption by Al-surrounding nano-cavities and silicon substrate at longer wavelengths. In contrast, reflection in transverse electric (TE) mode does not show distinct wavelength selectivity due to the cut-off effect of the nano-cavities. The outstanding characters of the proposed structure with polarization dependence, high sensitivity to incident angle, high color rendering facilitate more compact and sophisticated color-filter-based devices for displays, anti-counterfeit, and sensing applications. In addition, the two-dimensional structure with thin grating thickness and high duty ratio tolerance is relatively easy for fabrication

Broad bandwidth waveguide polarizer via grating mediated mode conversion

A polarization beam splitter (PBS) based on a four-layer slab waveguide is proposed, where a sub-wavelength grating is embedded between the waveguide core and the cladding. This grating not only affords Bragg momentum to tune the propagation constant of guiding modes but also converts the forward zero-order waveguide mode to the backward first one for a specific polarization. Thus, the incident light with polarization that satisfies the phase-matching condition is highly reflected in the waveguide, while other light with orthogonal polarization keeps intact and passes through it efficiently. Numerical simulations show that one can make the compact PBS for both polarizations with an extinction ratio higher than 35 dB, a waveband larger than 80 nm, a grating period tolerance of 20 nm, and a waveguide height tolerance of 80 nm. The revealed mode conversion mechanism via the sub-wavelength grating enriches the design of PBSs for integrated silicon waveguide chips

Highly tunable polarized chromatic plasmonic films based on sub-wavelength grating templates

A kind of polarized chromatic plasmonic film is proposed based on subwavelength grating structure, which enables “blue transmission” for the transverse electric light and “red transmission” for the transverse magnetic light. Metal–insulator–metal plasmonic waveguiding and metallic nanowire scattering are revealed to be responsible for the chromatic shift. Based upon the unique transmission spectrum characteristics of such films, polarized chromatic plasmonic tags (PCPTs) can be flexibly fabricated by patterning dielectric grating templates with designed figures and depositing appropriate thickness of metal. These PCPTs, simultaneously possessing directly visible unpolarized transmission colors and concealed distinct polarization‐dependent color shift, can be widely used as anti‐counterfeiting tags with higher security than the diffractive types of holograms

Analysis of an age-structured dengue model with multiple strains and cross immunity

Dengue fever is a typical mosquito-borne infectious disease, and four strains of it are currently found. Clinical medical research has shown that the infected person can provide life-long immunity against the strain after recovering from infection with one strain, but only provide partial and temporary immunity against other strains. On the basis of the complexity of transmission and the diversity of pathogens, in this paper, a multi-strain dengue transmission model with latency age and cross immunity age is proposed. We discuss the well-posedness of this model and give the terms of the basic reproduction number R0 = max{R1, R2} , where Ri is the basic reproduction number of strain i (i = 1, 2). Particularly, we obtain that the model always has a unique diseasefree equilibrium P0 which is locally stable for R0 1, the strain-i dominant equilibrium Pi is locally stable for Rj < R∗ i (i, j = 1, 2, i 6= j). Additionally, the threshold criteria on the uniformly persistence, the existence and global asymptotically stability of coexistence equilibrium are also obtained. Finally, these theoretical results and interesting conclusions are illustrated with some numerical simulations

Solar microwave millisecond spike at 2.84 GHz

Using the high time resolution of 1 ms, the data of solar microwave millisecond spike (MMS) event was recorded more than two hundred times at the frequency of 2.84 GHz at Beijing (Peking) Observatory since May 1981. A preliminary analysis was made. It can be seen from the data that the MMS-events have a variety of the fast activities such as the dispersed and isolated spikes, the clusters of the crowded spikes, the weak spikes superimposed on the noise background, and the phenomena of absorption. The marked differences from that observed with lower time resolution are presented. Using the data, a valuable statistical analysis was made. There are close correlations between MMS-events and hard X-ray bursts, and fast drifting bursts. The MMS events are highly dependent on the type of active regions and the magnetic field configuration. It seems to be crucial to find out the accurate positions on the active region where the MMS-events happen and to make co-operative observations at different bands during the special period when specific active regions appear on the solar disk