The State of NaOH in NaOH/Poly(Sodium Acrylate) Composite

NaOH/poly(sodium acrylate) composites were prepared by in situ polymerization of acrylic acid with an overneutralization level by adding excess NaOH. The composites were studied by XRD, IR and ²³Na MAS NMR spectroscopy. The results showed that the high neutralization degree (>100%) may lead to a complete polymerization. Both XRD and ²³Na MAS NMR spectra did not show any peaks of phase-separated NaOH or Na₂CO₃ until the neutralization degree was up to 217.5%. It can be presumed that the aggregates of Na⁺ ions can contain approximately two Na⁺ units for every carboxyl group before the phase separation.     

Curcumin Inhibits the Sortase A Activity of the Streptococcus mutans UA159

Streptococcus mutans (S. mutans) forms part of the commensal microflora and is deemed to be the major pathogen responsible for the generation of dental caries. The enzyme, sortase A enzyme, modulates the surface properties and cariogenicity of S. mutans. Curcumin has been reported to be an inhibitor of Staphylococcus aureus sortase A. In this study, inhibition of a purified S. mutans UA159 sortase A by curcumin was evaluated. Curcumin exerted strong inhibitory activity with a half maximal inhibitory concentration (IC₅₀) of 10.2?±?0.7 μM which was lower than the minimum inhibitory concentration of 175 μM and the minimum bactericidal concentration of 350 μM. These results indicated that curcumin is a S. mutans UA159 sortase A inhibitor and therefore represents as a promising anticaries agent.     

Validity of Inorganic Nanosheets as an Efficient Planar Substituent To Enhance the Enantioselectivity of Transition‐Metal‐Catalyzed Asymmetric Synthesis

Effectively enhancing the enantioselectivity is a persistent challenge in heterogeneous asymmetric catalysis. Here, the validity of a layered double hydroxides (LDH) nanosheet as an efficient planar substituent to enhance the enantioselectivity has been investigated theoretically; first in vanadium‐catalyzed asymmetric epoxidation of allylic alcohols, and then in zinc‐catalyzed direct asymmetric aldol addition. The computational predication is further confirmed experimentally in zinc‐catalyzed direct asymmetric aldol addition by controlling the location of catalytic sites.     

On a problem of Hornik

In 1991,Hornik proved that the collection of single hidden layer feedforward neural networks(SLFNs)with continuous,bounded,and non-constant activation functionσis dense in C(K)where K is a compact set in R~s(see Neural Networks,4(2),251-257(1991)).Meanwhile,he pointed out"Whether or not the continuity assumption can entirely be dropped is still an open quite challenging problem".This paper replies in the affirmative to the problem and proves that for bounded and continuous almost everywhere(a.e.)activation functionσon R,the collection of SLFNs is dense in C(K)if and only ifσis un-constant a.e..     

Photonic Floquet topological insulators in atomic ensembles

The feasibility of realizing a photonic Floquet topological insulator (PFTI) in an atomic ensemble is demonstrated. The interference of three coupling fields will split energy levels periodically, to form a periodic refractive index structure with honeycomb profile that can be adjusted by different frequency detunings and intensities of the coupling fields. This in turn will affect the appearance of Dirac cones in momentum space. When the honeycomb lattice sites are helically ordered along the propagation direction, gaps open at Dirac points, and one obtains a PFTI in an atomic vapor. An obliquely incident beam will be able to move along the zigzag edge of the lattice without scattering energy into the PFTI, due to the confinement of edge states. The appearance of Dirac cones and the formation of a photonic Floquet topological insulator can be shut down by the third‐order nonlinear susceptibility and opened up by the fifth‐order one.

     

Cylindrical invisibility cloak with simplified material parameters is inherently visible

It was proposed that perfect invisibility cloaks can be constructed for hiding objects from electromagnetic illumination [J. B. Pendry, D. Schurig, and D. R. Smith, Science 312, 1780 (2006)10.1126/science.1125907]. The cylindrical cloaks experimentally demonstrated [D. Schurig, Science 314, 977 (2006)10.1126/science.1133628] and theoretically proposed [W. Cai, Nat. Photon. 1, 224 (2007)10.1038/nphoton.2007.28] have however simplified material parameters in order to facilitate easier realization as well as to avoid infinities in optical constants. Here we show that the cylindrical cloaks with simplified material parameters inherently allow the zeroth-order cylindrical wave to pass through the cloak as if the cloak is made of a homogeneous isotropic medium, and thus visible. To all high-order cylindrical waves, our numerical simulation suggests that the simplified cloak inherits some properties of the ideal cloak, but finite scatterings exist.     

Ideal cylindrical cloak: perfect but sensitive to tiny perturbations

A cylindrical wave expansion method is developed to obtain the scattering field for an ideal two-dimensional cylindrical invisibility cloak. A near-ideal model of the invisibility cloak is set up to solve the boundary problem at the inner boundary of the cloak shell. We confirm that a cloak with the ideal material parameters is a perfect invisibility cloak by systematically studying the change of the scattering coefficients from the near-ideal case to the ideal one. However, because of the slow convergence of the zeroth-order scattering coefficients, a tiny perturbation on the cloak would induce a noticeable field scattering and penetration.     

Cavity linewidth narrowing and broadening due to competing linear and nonlinear dispersions

We experimentally demonstrate cavity linewidth control by manipulating dispersion of the intracavity medium. By making use of the dramatic change of Kerr nonlinearity near electromagnetically induced transparency resonance in a three-level atomic system, the cavity transmission linewidth can be greatly modified. As the cavity input intensity increases, the cavity linewidth changes from below to above empty cavity linewidth, corresponding to subluminal and superluminal photon propagation in the cavity, respectively.