Asymmetric synthesis of chromanone lactones via vinylogous conjugate addition of butenolide to 2-ester chromones

Chiral chromanone lactones are a class of natural products with important biological activity. We report a direct diastereo- and enantioselective vinylogous conjugate addition of butenolide to 2-ester substituted chromones. The transformation proceeded well in the presence of as low as 1 mol% of a chiral N,N′-dioxide/Sc^III complex, 3 Å MS and a catalytic amount of hexafluoroisopropanol (HFIP). The scope of Michael acceptors includes a variety of substituted chromones at different positions, and the desired chromanone lactones upon reduction are afforded in good yield and diastereoselectivity, and excellent enantioselectivity (up to 99% ee). The strategy could be used in the concise synthesis of blennolide C and gonytolide A, C and G.

We report a direct, diastero- and enantioselective vinylogous 1,4-addition of butanolide to 2-ester chromones. A chiral Sc^III complex enabled the reaction to proceed smoothly to give a variety of chraomanone lactones.     

Promote the conductivity of solid polymer electrolyte at room temperature by constructing a dual range ionic conduction path

Poly(ethylene oxide)(PEO) is a classic matrix model for solid polymer electrolyte which can not only dissociate lithium-ions(Li+),but also can conduct Li+through segmental motion in long-range.However,the crystal aggregation state of PEO restricts the conduction of Li⁺ especially at room temperature.In this work,an amorphous polymer electrolyte with ethylene oxide(EO) and propylene oxide(PO) block structure(B-PEG@DMC) synthesized by the transesterification is firstly obtained,showing ...     

Growth and raman scattering of aluminium gallium orthophosphate piezoelectric crystals

A new series of non-ferroelectric crystals, the piezoelectric solid solution aluminium gallium orthophosphate Al_1-xGa_xPO₄ (AGP, 0 < x < 1) system has been successfully developed by a hydrothermal method. The AGP crystal with X = 0.10 shows a phase transition temperature T_−β = 587 ± 3 °C with a cell parameters A = b = 0.49386(3) and C = 1.09563(2) nm. Raman spectra including directional dispersion in AGP are similar to those from -AIPO4 and -quartz crystals, indicating all of them belong to an isomorphic family, the short-range interaction being dominant in AGP. Comparison with -AIPO4 crystals, there exists an apparent red shift of the mode frequency and a smaller TO/LO mode splitting of the E species in the AGP crystals.     

A Method for Accurate Calculation ofB1Fields in Three Dimensions. Effects of Shield Geometry on Field Strength and Homogeneity in the Birdcage Coil

A method for calculatingB₁field strength and homogeneity as functions of radiofrequency shield geometry is presented. The method requires use of three-dimensional finite-element analysis, birdcage-coil theory, and antenna-array theory. Calculations were performed for a 12-element birdcage coil (19 cm diameter, 21 cm length) at 125 MHz. CalculatedB₁field strengths and homogeneities for the coil in 25 different shields and in no shield are given. For configurations where the shield is longer than the coil, bothB₁field strength and homogeneity decrease as shield diameter decreases or as shield length increases. In configurations where the shield is shorter than the coil and has a diameter of 25.6 cm,B₁homogeneity is greater than in an unshielded coil.B₁field strength was measured experimentally at 125 MHz in a birdcage coil of the same geometry as the model within shields of four different diameters. Calculated results very closely matched experimental measurement.     

An Active Set Modified Polak–Ribiére–Polyak Method for Large-Scale Nonlinear Bound Constrained Optimization

In this paper, we propose an active set modified Polak?CRibiére?CPolyak method for solving large-scale optimization with simple bounds on the variables. The active set is guessed by an identification technique at each iteration and the recently developed modified Polak?CRibiére?CPolyak method is used to update the variables with indices outside of the active set. Under appropriate conditions, we show that the proposed method is globally convergent. Numerical experiments are presented using box constrained problems in the CUTEr test problem libraries.     

Stochastic calculus for Markov processes associated with non-symmetric Dirichlet forms

Nakao’s stochastic integrals for continuous additive functionals of zero energy are extended from the symmetric Dirichlet forms setting to the non-symmetric Dirichlet forms setting.It? ’s formula in terms of the extended stochastic integrals is obtained.     

STEADY STATE BEHAVIOR OF A THREE-LEVEL ATOM IN A TWO-MODE PARAMETRICALLY DRIVEN CAVITY

We have studied the steady-state behavior of a cascade three-level atom in a two-mode bad cavity which is parametrically driven by a classical field. In the weak field limit, it has been found that the atomic population trapping in the upper-level depends on the cavity photon number not only linearly but also quadratically, and the atomic dipole squeezing can occur.     

Symplectic flow for the square root of the negative Laplacian

The paper is concerned with symplectic flow for the square root of the negative Laplacian, which is motivated when studying a one-dimensional model about ferromagnetic thin film without Gilbert damping term (only Gyromagnetic term remained) derived from the stationary model of A. DeSimone, R.V. Kohn, S. Müller and F. Otto. Existence of weak solution to the model is proved by viscosity approximation and commutator estimate.     

Quantum wells micro-ring resonator laser emitting at 1746 nm for gas sensing

Gas sensing for measurement of gas components, concentrations, and other parameters plays an important role in many fields. In this Letter, a micro-ring resonator laser used for gas sensing is experimentally demonstrated. The multi-quantumwells micro-ring laser based on whispering-gallery modes with an annular resonator and an output waveguide was fabricated. A single-mode laser with a wavelength of 1746.4 nm was fabricated for the first time, to the best of our knowledge,experimentally. The output power of 1.65 m W under 40 m A injection current was obtained with a side-mode suppression ratio over 33 d B.     

Double-slit diffraction of terahertz wave generated by tilted-pulse-front pumping

We propose a spatial diffraction diagnostic method via inserting a millimeter-gap double slit into the collimated terahertz beam to monitor the minute variation of the terahertz beam in strong-field terahertz sources, which is difficult to be resolved in conventional terahertz imaging systems. To verify the method, we intentionally fabricate tiny variations of the terahertz beam through tuning the iris for the infrared pumping beam before the tilted-pulse-front pumping setups.The phenomena can be well explained by the theory based on the tilted-pulse-front technique and terahertz diffraction.