Sealing materials for radio electronics

A review devoted to the sealants, adhesives, and compounds based on oligomers of variable classes that found wide application in radio electronics is presented. Their main operational characteristics, production technology, and peculiarities of utilization are described.     

Oscillations of the Critical Temperature in a (Fe/Cr/Fe)/V/Fe Heterostructure

The superconducting and magnetic properties of the (Fe/Cr/Fe)/V/Fe layered system with variable thickness of the chromium layer have been experimentally and theoretically studied. The magnetic properties of the system have been studied by the ferromagnetic resonance method, and the superconducting transition temperature has been measured from the jump in the magnetic susceptibility. A wide variety of magnetic states are observed in the system; in particular, the structure of small domains can arise in the iron layer placed between vanadium and chromium. It has been shown experimentally that the critical temperature T_c of the superconducting transition undergoes nonmonotonic oscillations with a noticeable amplitude in the given system with the change in the thickness of the Cr layer. The proposed model based on the proximity effect theory makes it possible to relate these T_c oscillations to the features of the magnetic structure of the samples.     

Diols Speed Up Guanidine Base Catalyzed Claisen-Schmidt Condensation to Produce New 15-Arylidene Steroids

Considerable acceleration was observed in the guanidine-base catalysed Claisen-Schmidt condensation of benzaldehyde and a 17α-methyl-18-nor-5α,13α-androstan-16-one ( 1 ) in the presence of ethylene glycol. Rate-enhancement effects of various alcohols and diols were compared. In quantum chemical calculations, coordination of the carbonyl group of the substrate was found to reduce the potential barrier to the proton transfer from the α carbon and thus facilitate the formation of the anion that attacks the aldehyde. Both the experiments and the calculations showed that diols enhance the reactivity more efficiently than alcohols. Ethylene glycol/guanidine-base mixtures were found to be efficient catalysts and solvents in the synthesis of a range of new 17α-methyl-18-nor-13α-15-arylidene steroids. This solvent mixture has a further advantage: the crude products can be isolated by simple extraction after introduction of CO₂. It is also shown that by the proper choice of the base, the base/diol mixture can be recycled.     

Extremal discs and holomorphic extension from convex hypersurfaces

Let D be a convex domain with smooth boundary in complex space and let f be a continuous function on the boundary of D. Suppose that f holomorphically extends to the extremal discs tangent to a convex subdomain of D. We prove that f holomorphically extends to D. The result partially answers a conjecture by Globevnik and Stout of 1991.     

Influence of pyrogenic silica hydration on water diffusion in surface layers

The surface hydration of pyrogenic silica (aerosil) has been studied by slow neutron scattering. It was shown that the rate of diffusion changes with the thickness of the layer monotonically. The mean square displacement of water molecules from the equilibrium position in aerosil hydration shell is smaller than in bulk water, but twice larger than in ice.     

On relativistic wave equations

A method is given for obtaining relativistic wave equations in matrix form for particles with higher spins. Values are given for the constants of the ^v matrices, the matrix of the inversion operator, and the scalar matrix which enters into the expression of the current for particles with spin 0, 1/2, 1, 3/2, or 2.     

Controlled Generation of 9‐Boratriptycene by Lewis Adduct Dissociation: Accessing a Non‐Planar Triarylborane

A highly bent triarylborane, 9‐boratriptycene, was generated in solution by selective protodeboronation of the corresponding tetra‐aryl boron ate complex with the strong Brønsted acid HNTf₂. The iptycene core confers enhanced Lewis acidity to 9‐boratriptycene, making it unique in terms of structure and reactivity. We studied the stereoelectronic properties of 9‐boratriptycene by quantifying its association with small N‐ and O‐centered Lewis bases, as well as with sterically hindered phosphines. The resultant Lewis adducts exhibited unique structural, spectroscopic, and photophysical properties. Beyond the high pyramidalization of the 9‐boratriptycene scaffold and its low reorganization energy upon Lewis base coordination, quantum chemical calculations revealed that the absence of π donation from the triptycene aryl rings to the boron vacant p_z orbital is one of the main reasons for its high Lewis acidity.