Novel Photochemical Rearrangement of Styrylfurans

A conrotatory photocyclization , a novel [1,9] hydrogen shift, and a lateral ring opening are involved in the rearrangement of a series of 2-(4-alkylstyryl)furans 1 to 5-(3-alkylbutadienyl)benzo[b]furans 2 in dichloromethane. These novel photochemical rearrangements occur with good yields of isolated products.     

Mechanism on oscillating lifted flames in nonpremixed laminar coflow jets

The oscillating lifted flame in a laminar nonpremixed nitrogen-diluted fuel jet is known to be a result of buoyancy, though the detailed physical mechanism of the initiation has not yet been properly addressed. We designed a systematic experiment to test the hypothesis that the oscillation is driven by competition between the positive buoyancy of flame and the negative buoyancy of a fuel stream heavier than the ambient air. The positive buoyancy was examined with various flame temperatures by changing fuel mole fraction, and the negative buoyancy was investigated with various fuel densities. The density of the coflow was also varied within a certain range by adding either helium or carbon dioxide to air, to study how it affected the positive and negative buoyancies at the same time. As a result, we found that the range of oscillation was well-correlated with the positive and the negative buoyancies; the former stabilized the oscillation while the latter triggered instability and became a source of the oscillation. Further measurements of the flow fields and OH radicals evidenced the important role of the negative buoyancy on the oscillation, detailing a periodic variation in the unburned flow velocity that affected the displacement of the flame.     

Finite-/fixed-time robust stabilization of switched discontinuous systems with disturbances

Nonlinear Dynamics - This paper investigates the finite-time and fixed-time stabilization (FFTS) of switched systems with discontinuous dynamics, external disturbances and delays. Firstly, a new...     

Highly Bright and Photostable Li(Gd,Y)F4:Yb,Er/LiGdF4 Core/Shell Upconversion Nanophosphors for Bioimaging Applications

Intense green‐emitting Li(Gd,Y)F₄:Yb,Er/LiGdF₄ core/shell (C/S) upconversion nanophosphors (UCNPs) with a tetragonal bipyramidal morphology are synthesized. The morphology and UC luminescence of the Li(Gd,Y)F₄:Yb,Er UCNPs are significantly affected by the Li precursors, and bright UC green‐emitting Li(Gd,Y)F₄:Yb,Er UCNPs with a tetragonal bipyramidal shape, i.e., UC tetragonal bipyramids (UCTBs), are synthesized using LiOH·H₂O as a Li precursor. A LiGdF₄ shell is grown on the Li(Gd,Y)F₄:Yb,Er UCTBs, and the C/S UCNPs exhibit 4.7 times higher luminescence intensity than core UCTBs. The C/S UCNPs show a high absolute UC quantum yield of 4.6% under excitation with 980 nm near infrared (NIR) light, and the UC luminescence from the C/S UCNPs is stable under continuous irradiation with the 980 nm NIR laser for 1 h. The hydrophobic surfaces of the as‐synthesized C/S UCNPs are modified to hydrophilic surfaces by using poly(acrylic acid) (PAA) for bioimaging applications. They are applied to human cervical adenocarcinoma (HeLa) cell imaging and SK‐MEL‐2 melanoma cell imaging and in vivo imaging, including subcutaneous and intramuscular imaging, and UC luminescence images with high signal‐to‐noise ratio are obtained. Furthermore, sentinel‐lymph‐node imaging is successfully conducted with the PAA‐capped Li(Gd,Y)F₄:Yb,Er/LiGdF₄ C/S UCNPs under illumination with NIR light.     

Multiparameter kinetic analysis of alkaline hydrolysis of a series of aryl diphenylphosphinothioates: models for P=S neurotoxins

Alkaline hydrolysis of a series of X‐substituted‐phenyl diphenylphosphinothioates ( 2a‐i ) in 80 mol%/20 mol% DMSO at 25.0 ± 0.1°C has been studied kinetically and assessed through a multiparameter approach. Substrates 2a to 2i are approximately 12 to 22 times less reactive than their P=O analogues 1a to 1i (ie, the thio effect). The Brønsted‐type plot for the reactions of 2a to 2i is linear with β_lg = ?0.43, consistent with a concerted mechanism. Hammett plots correlated with σ^o and σ^? constants also support a concerted mechanism; the Yukawa‐Tsuno plot results in an excellent linear correlation with ρ_X = 1.26 and r = 0.30, indicating that expulsion of the leaving group occurs in the rate‐determining step (RDS). The ΔH^? value increases from 10.5 to 11.7 and 13.9 kcal/mol as substituent X in the leaving group changes from 3,4‐(NO₂)₂ to 4‐NO₂ and H, in turn, while TΔS^? remains constant at ?6.0 kcal/mol. The strong dependence of ΔH^? on the electronic nature of substituent X also indicates that the leaving group departs in the RDS. The reaction mechanism and origin of the thio effect are discussed by comparison of the current kinetic results with those reported for the reactions of 1a to 1i . The results suggest that for useful OP neurotoxins the mechanism of abiotic hydrolysis is concerted (with varying degrees of asynchronicity) when the substrate bears good leaving groups.     

Electric Field‐Aided Formation Combined with a Nanoimprinting Technique for Replicating a Plant Leaf

The surface of the taro plant leaf was replicated using a nanoimprinting technique (NIT) supplemented with an electric field. This field‐aided nanoimprinting method (FA‐NIT) consists of two steps: applying an electric field to a liquid polymer under the plant leaves and the curing process of the polymer with the applied electric field. An appropriate electric field was needed to induce the electrokinetic phenomena of a liquid polymer to obtain a good replicated surface. The roughness fabricated by the FA‐NIT was about 45% higher than the one prepared by NIT. The FA‐NIT method is a good supplementary technique to improve the quality of NIT.

     

Discriminating Among Co‐monomer Sequence Distributions in Random Copolymers Using Interaction Chromatography

Interaction chromatography has been employed to validate that adsorption of poly[styrene‐co‐(4‐bromostyrene)] (PBr_xS) random copolymers, where x denotes the mole fraction of 4‐bromostyrene (4–BrS) in PBr_xS in solution depends on the average number of adsorptive segments, the type of adsorbing substrate, and on the co‐monomer sequence distribution in PBr_xS.

     

Synthesis of Eu x Si6? z Al z O z N8? z green phosphor and?its?luminescent properties

Rare-earth-doped oxynitride or nitride compounds have been reported to be photoluminescent and may then serve as new phosphors because of their good thermal and chemical stabilities. In this work, Eu²⁺-doped β-SiAlON phosphor with a composition of Eu _x Si_6−z Al _z O _z N_8−z (x=0.018, z=0.23) was prepared by gas-pressured solid state reaction. The crystallinity and particle morphology of the prepared phosphor were characterized. The Stokes shift and zero-phonon line were calculated mathematically and estimated from the spectral data. The temperature dependence of photoluminescence was measured from 25 to 250°C. The prepared Eu²⁺-doped β-SiAlON green phosphor showed superior thermal quenching property compared to silicate (SrBaSiO₄:Eu²⁺) green phosphor. The white light-emitting diode (LED) back-lighting unit (BLU) using the prepared β-SiAlON:Eu²⁺ green phosphor exhibited higher color gamut than a commercial silicate phosphor.     

A strip-shield improves the efficiency of a solenoid coil in probes for high-field solid-state NMR of lossy biological samples

A strip-shield inserted between a high inductance double-tuned solenoid coil and the glass tube containing the sample improves the efficiency of probes used for high-field solid-state NMR experiments on lossy aqueous samples of proteins and other biopolymers. A strip-shield is a coil liner consisting of thin copper strips layered on a PTFE (polytetrafluoroethylene) insulator. With lossy samples, the shift in tuning frequency is smaller, the reduction in Q, and RF-induced heating are all significantly reduced when the strip-shield is present. The performance of 800 MHz ¹H/¹⁵N and ¹H/¹³C double-resonance probes is demonstrated on aqueous samples of membrane proteins in phospholipid bilayers.