Microextraction of 17-β-Estradiol from Medicinal Preparations for the Subsequent Determination by HPLC-UV

Journal of Analytical Chemistry - A method is proposed for the chromatographic determination of 17-β-estradiol in medicinal preparations with the microextraction of the analyte from a sample...     

Analytical Solutions of the Equation Describing Internal Gravity Waves Generated by a Moving Nonlocal Source of Perturbations

Computational Mathematics and Mathematical Physics - The problem of constructing analytical solutions describing internal gravity wave fields generated by a nonlocal source of perturbations moving...     

Noncovalent Axial I⋅⋅⋅Pt⋅⋅⋅I Interactions in Platinum(II) Complexes Strengthen in the Excited State

Coordination compounds of platinum(II) participate in various noncovalent axial interactions involving metal center. Weakly bound axial ligands can be electrophilic or nucleophilic; however, interactions with nucleophiles are compromised by electron density clashing. Consequently, simultaneous axial interaction of platinum(II) with two nucleophilic ligands is almost unprecedented. Herein, we report structural and computational study of a platinum(II) complex possessing such intramolecular noncovalent I⋅⋅⋅Pt⋅⋅⋅I interactions. Structural analysis indicates that the two iodine atoms approach the platinum(II) center in a “side-on” fashion and act as nucleophilic ligands. According to computational studies, the interactions are dispersive, weak and anti-cooperative in the ground electronic state, but strengthen substantially and become partially covalent and cooperative in the lowest excited state. Strengthening of I⋅⋅⋅Pt⋅⋅⋅I contacts in the excited state is also predicted for the sole previously reported complex with analogous axial interactions.     

A non-singular continuum theory of dislocations

We develop a non-singular, self-consistent framework for computing the stress field and the total elastic energy of a general dislocation microstructure. The expressions are self-consistent in that the driving force defined as the negative derivative of the total energy with respect to the dislocation position, is equal to the force produced by stress, through the Peach-Koehler formula. The singularity intrinsic to the classical continuum theory is removed here by spreading the Burgers vector isotropically about every point on the dislocation line using a spreading function characterized by a single parameter a, the spreading radius. A particular form of the spreading function chosen here leads to simple analytic formulations for stress produced by straight dislocation segments, segment self and interaction energies, and forces on the segments. For any value a>0, the total energy and the stress remain finite everywhere, including on the dislocation lines themselves. Furthermore, the well-known singular expressions are recovered for a=0. The value of the spreading radius a can be selected for numerical convenience, to reduce the stiffness of the dislocation equations of motion. Alternatively, a can be chosen to match the atomistic and continuum energies of dislocation configurations.     

Analytical Solutions of the Internal Gravity Wave Equation in a Stratified Medium with Shear Flows

Computational Mathematics and Mathematical Physics - The problem of constructing internal gravity wave fields generated by an oscillating localized point source of disturbances in a stratified...     

An analysis of multistep methods for solving integral-algebraic equations: Construction of stability domains

Systems of Volterra integral equations with identically singular matrices in the principal part (called integral-algebraic equations) are examined. Multistep methods for the numerical solution of a selected class of such systems are proposed and examined.     

Investigating iron ion distribution in (Y3 − x Ca x )3Fe5)12 garnets as a function of Ca2+ content

Ferrite garnets have special physical properties associated with the valence of obtained ions. These properties can be studied only by precise structural analysis and the determining the ions’ valency.     

On a family of singular integro-differential equations

Integro-differential systems in which the matrix multiplying the derivative of the unknown vector function is identically singular are analyzed. This analysis is based on the special properties of the matrix polynomials associated with the original system. An existence theorem is proved, and a numerical method for finding the solution is proposed and justified.     

Formation of submicron partially ordered domain structures in ferroelectric and magnetic materials

Formation of domains and partially ordered periodic domain structures in ferroelectric and magnetic oxides of metals of transition groups has been investigated. Physical features of appearance of submicron periodic domain structures and possibilities of their use for the control over the parameters of high-frequency acoustic waves have been considered using the example of single crystals of lithium niobate and lanthanum-strontium manganites.