A switchable perfect absorber with multispectral thermal imaging capability is presented. Aluminum nanoantenna arrays above a germanium antimony telluride (GST) spacer layer and aluminum mirror provide efficient wavelength-tunable absorption in the mid-infrared. Utilizing the amorphous-to-crystalline phase transition in GST, this device offers switchable absorption with strong reflectance contrast at resonance and large phase-change-induced spectral shifts.

h i g h l i g h t sAnthropogenic and biogenic organic compounds have been studied in PM 2.5 in Beijing. Higher levels of organic species were found in the upwind Yufa than PKU. Biogenic secondary organic carbon accounts for 3.1% of OC at PKU and 5.2% at Yufa. a r t i c l e i n f o a b s t r a c tAmbient fine aerosol samples (PM 2.5 ) were collected at an urban site (PKU) in Beijing and its upwind suburban site (Yufa) during the CAREBEIJING-2007 field campaign. Organic molecular compositions of the PM 2.5 samples were studied for seven organic compound classes (sugars, lignin/resin acids, hydroxy-/ polyacids, aromatic acids, biogenic SOA tracers, fatty acids and phthalates) using capillary GC/MS to better understand the characteristics and sources of organic aerosol pollution in Beijing. More than 60 individual organic species were detected in PM 2.5 and were grouped into different compound classes based on their functional groups. Concentrations of total quantified organics at Yufa (469e1410 ng m À3 , average 1050 ng m À3 ) were slightly higher than those at PKU (523e1390 ng m À3 , 900 ng m À3 ). At both sites, phthalates were found as the most abundant compound class. Using a tracer-based method, the contributions of the biogenic secondary organic carbon (SOC) to organic carbon (OC) were 3.1% at PKU and 5.5% at Yufa, among which isoprene-SOC was the dominant contributor. In addition, most of the measured organic compounds were higher at Yufa than those at PKU, indicating a more serious pollution in its upwind region than in urban Beijing.

We will discuss fabrication of twin core photonic crystal fiber (TC-PCF) using the stack-and-draw method and its application for in-line Mach-Zehnder interferometers. The small difference in the effective indexes of the two core modes leads to interference fringes and the birefringence of the twin cores results in polarization-dependent fringe spacing. The strain sensitivity was negative and wavelength-dependent. A novel intensity-based bend sensor is also demonstrated with bend-induced spatial fringe shift. High air filling fraction of fabricated TC-PCF cladding provides immunity to bend-induced intensity fluctuation.

A covalent adaptable network can endow rubber materials with recyclability and reprocessability and is expected to alleviate black pollution caused by end-of-life rubber. However, the loss of traditional vulcanization systems severely sacrifices their strength, and the tensile strength in the current study rarely exceeds 10 MPa unless fillers are added. In this work, we proposed a self-strengthening process based on dual-dynamic units (imine and disulfide), briefly, under heating, phenylsulfur radicals generated from aromatic disulfide bonds can react with double bonds (mostly vinyl) and/or couple with allyl sites, thus reforming a stronger cross-linked network. The neighboring imine unit is not affected and provides excellent thermal reprocessability and chemical recyclability. The result shows that the tensile strength can reach 19.27 MPa via self-strengthening without adding fillers or any other additives, and this ultra-high-strength is much higher than those of all known recyclable polybutadiene-based rubber materials. In addition, the material also has malleability, shape memory, and self-welding properties. By doping carbon nanotubes, a recyclable conductive composite can also be achieved. In general, we envision that this enhanced strategy has great potential to be generalized for all elastomers containing double bonds (such as styrene–butadiene rubber, nitrile rubber, isoprene rubber, and their derivatives). The reprocessability and self-welding are practical for on-site assembly or repair of composite parts and extend the service life of materials.