Synthesis of a New 10,11-Didehydro Analog of Epothilone D

Russian Journal of Organic Chemistry - A new chiral 10,11-didehydro analog of epothilone D with isosteric substitution in the C15–C3 fragment of natural epothilones has been synthesized.     

Radial Domains in DyPr–FeCo–B Microwires

Physics of the Solid State - In DyPr–FeCo–B microwires with easy magnetization axis directed along the microwire axis, domains with radial magnetization are detected using...     

Magneto-Optical Properties and Photoluminescence of (PrDy)(FeCo)B Microwires

Physics of the Solid State - Microwires (PrDy)(FeCo)B, containing no iron inclusions and nuclei, are obtained by extraction from a drop of (PrDy)(FeCo)B melt at a reduced cooling rate. Inclusions...     

Effect of electronic polarization on charge-transport parameters in molecular organic semiconductors

Theoretical investigations of charge transport in organic materials are generally based on the "energy splitting in dimer" method and routinely assume that the transport parameters (site energies and transfer integrals) determined from monomer and dimer calculations can be reliably used to describe extended systems. Here, we demonstrate that this transferability can fail even in molecular crystals with weak van der Waals intermolecular interactions, due to the substantial (but often ignored) impact of polarization effects, particularly on the site energies. We show that the neglect of electronic polarization leads to qualitatively incorrect values and trends for the transfer integrals computed with the energy splitting method, even in simple prototypes such as ethylene or pentacene dimers. The polarization effect in these systems is largely electrostatic in nature and can change dramatically upon transition from a dimer to an extended system. For example, the difference in site energy for a prototypical "face-to-edge" one-dimensional stack of pentacene molecules is calculated to be 30% greater than that in the "face-to-edge" dimer, whereas the site energy difference in the pentacene crystal is vanishingly small. Importantly, when computed directly in the framework of localized monomer orbitals, the transfer integral values for dimer and extended systems are very similar.     

Transformation of C4-Methyl Derivatives of Levoglucosenone to 2,5-Dihydrofurans. An Unexpected Intramolecular Oxacyclization

Russian Journal of Organic Chemistry - The acid-catalyzed reaction of C4-methyl derivatives of levoglucosenone with ethanethiol and propane-1,3-dithiol was studied. The reaction takes a nontrivial...     

Photoelectric Properties of Composite Si Layers with Ag Nanoparticles Obtained by Ion Implantation and Laser Annealing

Optics and Spectroscopy - Structural and photoelectric properties of composite Ag:Si layers formed in the near-surface area of a single-crystal c-Si substrate by a high-dose implantation of Ag+...     

Systems with Discontinuous Quasi-Zero Reconstructing Force

The paper deals with the problem of constructing systems with discontinuous quasizero reconstructing force on the basis of structures where an elastic element moves between two directrices of prescribed design shape perpendicularly to their axis of symmetry. A spring is considered as an elastic element. The cases where the elastic element works only in compression or only in tension are considered.     

Investigation of the Solutions of Linear Systems of Difference Equations with Random Coefficients

The aim of the present paper is to give an equation which defines the moments equations for the solutions of linear systems of difference equations with random coefficients. Further we consider the cases when the coefficients depend on or do not depend on a Markov chain. Moreover, we investigate the stability of the null solutions for a linear system of difference equations in the mean and in the mean square.     

Correlation of Electronic and Magnetic Properties of Thin Polymer Layers with Cobalt Nanoparticles

Nanoparticles (NPs) of cobalt are synthesized in shallow layers of polyimide using 40 keV implantation of Co⁺ ions with a few different fluences at various ion current densities. Nucleation of individual NPs at low fluencies and their percolation at high fluencies are crucial processes governing the electrical and magnetic properties of the metal/polymer nanocomposites that can be controlled by the implantation regimes. In particular, one can tune the magnetoresistance between negative and positive through appropriate choice of ion fluence and current density. The found non‐monotonous dependence of the magnetoresistance on the applied magnetic field allows suggestion of spin‐dependent domain wall scattering affecting the electron transport. The samples implanted with low fluencies demonstrate superparamagnetic behavior down to very low blocking temperatures. For high fluence (1.25 × 10¹⁷ cm⁻²) the transition to ferromagnetic ordering is observed that is related to the increased magnetic interaction of NPs.