Weak solutions for a bi-fluid model for a mixture of two compressible non interacting fluids

Science China Mathematics - We investigate a version of one velocity Baer-Nunziato model with dissipation for the mixture of two compressible fluids with the goal to prove for it the existence of...     

Gas-phase dynamics of spiropyran and spirooxazine molecules

The gas-phase dynamics of two classes of photochromic molecules, three spiropyrans and one spirooxazine, have been investigated here using both time-resolved mass spectrometry and photoelectron spectroscopy approaches. It is, to our knowledge, the first gas-phase experiment done of these kinds of molecules. The molecules are excited at 266 nm and probed at 800 nm. The comparison of the dynamics of these four molecules has been used to propose a sequential photoisomerization mechanism involving four steps occurring in the first 100 ps. Each of these steps is discussed and related to the observed condensed-phase dynamics and to theoretical calculations.     

Revisiting Energy Release Rates in Brittle Fracture

We revisit in a 2d setting the notion of energy release rate, which plays a pivotal role in brittle fracture. Through a blow-up method, we extend that notion to crack patterns which are merely closed sets connected to the crack tip. As an application, we demonstrate that, modulo a simple meta-stability principle, a moving crack cannot generically kink while growing continuously in time. This last result potentially renders obsolete in our opinion a longstanding debate in fracture mechanics on the correct criterion for kinking.     

Dichloroenol Ethers X-ray Analysis in the Mechanistic Elucidation of Ynol Ethers Formation

Abstract  

X-ray crystallographic data are provided for dichloroenol ethers (S,E)-2-(1-(1,2-dichlorovinyloxy)ethyl)-1,3,5-triisopropylbenzene (2) and (S,E)-2-(1-(1,2-dichloroprop-1-enyloxy)ethyl)-1,3,5-triisopropylbenzene (3). The former forms colorless crystals (orthorhombic, P2₁2₁2₁ space group) and exhibits the following cell parameters: a = 10.212(5) ?; b = 10.359(8) ?; c = 18.217(6) ?. The latter also affords colorless crystals (monoclinic, P2₁ space group) with a = 13.558(2) ?; b = 10.891(1) ?; c = 15.260(2) ?; β = 115.65(1)°. The data complement those recently reported for two other dichloroenol ethers, ((1R,2S)-2-((E)-1,2-dichlorovinyloxy)cyclohexyl)benzene (5) and ((1R,2S)-2-((E)-1,2-dichloroprop-1-enyloxy)cyclohexyl)benzene (6). The X-ray analyses of these dichloroenol ethers, the only reported to date, establish unambiguously the trans stereochemistry of the chlorides in these and, by extension, similarly prepared enol ethers. This information was required for the complete mechanistic understanding of ynol ethers formation from dichloroenol ethers. Structural comparison of these dichloroenol ethers with some carbon (dichloroalkene) and nitrogen (dichloroenamine) analogues is also presented.     

Impact dynamics for elastic membranes

We study the dynamic response of stretched thin polymeric films following an impact by a rigid sphere. We vary the sphere radius, the impact velocity, and the film tension, and measure the contact time and the maximum deflection of the film during the impact. The response is sensitive to nonlinearities associated with the additional tension provided by the deformation. A physical model at the scaling level is presented. This allows us (i) to understand qualitatively experimental and numerical results and (ii) to present a diagram mapping different possible impact dynamics for membrane systems, which accounts for the interplay between membrane tension, intrinsic modulus, and geometrical factors such as the frame size and the sphere radius.     

Asymmetric [2 + 2] cycloaddition: total synthesis of (-)-swainsonine and (+)-6-epicastanospermine

[reaction: see text] An asymmetric total synthesis of (-)-swainsonine and (+)-6-epicastanospermine is described from a common intermediate, which is obtained through diastereoselective [2 + 2] cycloaddition of dichloroketene to a chiral enol ether.     

Sol–gel preparation of aminopropyl-silica-magnesia hybrid materials

A series of aminopropyl-silica-magnesia hybrid materials has been prepared by the sol–gel method from tetraethoxysilane (TEOS), magnesium chloride (MgCl₂) and aminopropyltriethoxysilane (APTES) under acid conditions. The APTES:TEOS ratio was varied between 0:1 and 1:0. The aminopropyl coverage concentrations for APTES-silica-Mg samples were in the range of 0.3–2.3 mmol g⁻¹. The hybrid materials were characterized by numerous techniques, including X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Fourier transform Raman spectroscopy (FT-Raman), solid-state ¹³C and ²⁹Si nuclear magnetic resonance (¹³C- and ²⁹Si-NMR), thermogravimetry (TGA), N₂ adsorption–desorption, small-angle X-ray scattering (SAXS), and scanning electron microscopy (SEM). The increase of APTES content in the silica network resulted in the increase of six-membered siloxane rings. The hybrid systems were shown to be formed from fully-condensed, trifunctional APTES species. The porosity and morphology of the hybrid materials were influenced by the initial TEOS/APTES ratio. The radius of gyration of the primary particles, determined by SAXS, was between 1.1 and 2.9 nm.     

An unprecedented 7-membered ring enamide cyclization through hypervalent iodine phenolic oxidation

An unprecedented 7-membered ring cyclization of an enamide to a phenol through hypervalent iodine phenolic oxidation was discovered. In the process a molecule of solvent is incorporated on the cycle forming an unusual and stable hemi-aminal ether.