Sequential centrifugal layer chromatography (SCLC): A new technique for the isolation of natural compounds. Part 2: Comparative study on centrifugal layer chromatography (CLC) and SCLC for the separation of furocoumarin isomers

The new sequential centrifugal layer chromatography extends the possibilities for preparative separation of furocoumarin isomers. In the present work, isobergapten, pimpinellin, bergapten, isopimpinellin, and sphondin were isolated from a prepurified extract of Heracleum sphondylium roots using two different techniques, namely, centrifugal layer chromatography (CLC) and sequential centrifugal layer chromatography (SCLC). The former technique was carried out with four plates, whereas the latter method required only one plate, using the same mobile phase in each case. A further advantage of the SCLC method was that all completely separated compounds could be quickly and efficiently eluted in small volumes of mehtanol.     

Surfactant in the gaseous phase II. Influence on stability of foams and thin liquid films

The influence of the vapors ofn-amyl orn-decyl alcohol on the stability of single thin liquid films, single bubbles, and foam columns was determined. It was found that the presence of surfactant vapors lowered the stability of foams and single foam films. The mechanism of the destabilizing action of the surfactant vapors on wet, dynamic foams under dynamic conditions is discussed. It is shown that the destabilizing action of the surfactant vapors is a further indication that surface elasticity forces are the main factor determining stability of wet, dynamic foams.     

线弹性问题的一个四面体元分析

构造了一个新的locking-free非协调四面体元,研究了单元对三维纯位移弹性问题的一致收敛性,得到了最优的误差估计结果.     

Surface effects in the deformation of an anisotropic elastic material with nano-sized elliptical hole

We examine the effect of surface energy on an anisotropic elastic material weakened by an elliptical hole. A closed-form, full-field solution is derived using the standard Stroh formalism. In particular, explicit expressions for the hoop stress, normal, in-plane tangential and out-of-plane displacement components along the edge of the hole are obtained. These expressions clearly demonstrate the effect of elastic anisotropy of the bulk material on the corresponding field variables. When the material becomes isotropic, the hoop stress agrees with the well-known result in the literature while both the in-plane tangential and out-of-plane displacements vanish and the normal displacement is constant along the entire boundary of the elliptical hole.     

Calix[4]pyrrolato Aluminates: The Effect of Ligand Modification on the Reactivity of Square-Planar Aluminum Anions

Structural constraint represents an attractive tool to modify p-block element properties without the need for unusual oxidation or valence states. The recently reported methyl-calix[4]pyrrolato aluminate established the effect of forcing a tetrahedral aluminum anion into a square-planar coordination mode. However, the generality of this structural motif and any consequence of ligand modification remained open. Herein, a systematic ligand screening was launched, and the class of square-planar aluminum anions was extended by two derivatives that differ in the meso-substitution at the calix[4]pyrrolato ligand. Strikingly, this modification provoked opposing trends in the preference for a Lewis acidic binding mode with σ-donors versus the aluminum-ligand cooperative binding mode with carbonyls. Insights into the origin of these counterintuitive experimental observations were provided by computation and bond analysis. Importantly, this rationale might allow to exploit mode-selective binding for catalytic rate control.     

Synthesis and characterization of intrinsic high‐barrier polyimide derived from a novel diamine monomer containing rigid planar moiety

A new diamine monomer containing rigid planar fluorenone moiety, 2,7‐bis(4‐aminophenyl)‐9H‐fluoren‐9‐one, was synthesized through Suzuki coupling reaction. Then it was reacted with pyromellitic dianhydride to obtain a polyimide (FOPPI) via a conventional two‐step polymerization process. The prepared FOPPI exhibits excellent barrier properties, with the oxygen transmission rate and water vapor transmission rate low to 3.2 cm³·m^?2·day^?1 and 2.9 g·m^?2·day^?1, respectively. The results of wide angle X‐ray diffractograms, positron annihilation lifetime spectroscopy, and molecular dynamics simulations reveal that the excellent barrier properties of FOPPI are mainly ascribed to the crystallinity, high chain rigidity, and low free volume, which are resulted from the rigid planar moiety. FOPPI also shows outstanding thermal stability and mechanical properties with a glass transition temperature up to 420 °C, 5% loss temperature of 607 °C, coefficient of thermal expansion of 1.28 ppm K^?1, and tensile strength of 150.8 MPa. The polyimide has an attractive potential application prospect in the flexible electronics encapsulation area. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 2373–2382     

Accurate Measurement of a Small Defect in a Planar Waveguide

Abstract

A non-destructive test method of a small defect (a dust particle or an air bubble) in a strongly confined planar waveguide is demonstrated in this work. Based on strong resonances between the small defect and some special incident wavelengths, an accurate reconstruction of the defect parameters can quickly be obtained from our previous numerical method. An example is given to verify the validity of the present measurement method.     

Planar Digraphs of Digirth Five Are 2‐Colorable

Neumann‐Lara (1985) and ?krekovski conjectured that every planar digraph with digirth at least three is 2‐colorable, meaning that the vertices can be 2‐colored without creating any monochromatic directed cycles. We prove a relaxed version of this conjecture: every planar digraph of digirth at least five is 2‐colorable. The result also holds in the setting of list colorings.     

Bi-Sobolev solutions to the prescribed Jacobian inequality in the plane with Lp data and applications to nonlinear elasticity

We construct planar bi-Sobolev mappings whose local volume distortion is bounded from below by a given function $f\in L^p$ with $p>1$. More precisely, for any $1<q<(p+1)/2$ we construct $W^{1,q}$-bi-Sobolev maps with identity boundary conditions; for $f\in L^{\infty }$, we provide bi-Lipschitz maps. The basic building block of our construction are bi-Lipschitz maps which stretch a given compact subset of the unit square by a given factor while preserving the boundary. The construction of these stretching maps relies on a slight strengthening of the celebrated covering result of Alberti, Csörnyei, and Preiss for measurable planar sets in the case of compact sets. We apply our result to a model functional in nonlinear elasticity, the integrand of which features fast blowup as the Jacobian determinant of the deformation becomes small. For such functionals, the derivation of the equilibrium equations for minimizers requires an additional regularization of test functions, which our maps provide.