Development of electrodynamic methods for calculation of printed dipole antennas based on multilayer dielectric structures

We found a solution for the electrodynamic problem of calculating the main characteristics (input resistance, radiation pattern, and directive gain) of a printed dipole radiator located in a no-loss multilayer dielectric structure (MDS). Rostov State University, Rostov-on-Don, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 6, pp. 551–560, June 1999.     

Tetrathiafulvalene‐amido‐2‐pyridine‐N‐oxide as Efficient Charge‐Transfer Antenna Ligand for the Sensitization of YbIII Luminescence in a Series of Lanthanide Paramagnetic Coordination Complexes

The tetrathiafulvalene‐amido‐2‐pyridine‐N‐oxide ( L ) ligand has been employed to coordinate 4f elements. The architecture of the complexes mainly depends on the ionic radii of the lanthanides. Thus, the reaction of L in the same experimental protocol leads to three different molecular structure series. Binuclear [Ln₂(hfac)₅(O₂CPhCl)( L )₃] ? 2 H₂O (hfac^?=1,1,1,5,5,5‐hexafluoroacetylacetonate anion, O₂CPhCl^?=3‐chlorobenzoate anion) and mononuclear [Ln(hfac)₃( L )₂] complexes were obtained by using rare‐earth ions with either large (Ln^III=Pr, Gd) or small (Ln^III=Y, Yb) ionic radius, respectively, whereas the use of Tb^III that possesses an intermediate ionic radius led to the formation of a binuclear complex of formula [Tb₂(hfac)₄(O₂CPhCl)₂( L )₂]. Antiferromagnetic interactions have been observed in the three dinuclear compounds by using an extended empirical method. Photophysical properties of the coordination complexes have been studied by solid‐state absorption spectroscopy, whereas time‐dependent density functional theory (TD‐DFT) calculations have been carried out on the diamagnetic Y^III derivative to build a molecular orbital diagram and to reproduce the absorption spectrum. For the [Yb(hfac)₃( L )₂] complex, the excitation at 19 600 cm^?1 of the HOMO→LUMO+1/LUMO+2 charge‐transfer transition induces both line‐shape emissions in the near‐IR spectral range assigned to the ²F_5/2→²F_7/2 (9860 cm^?1) ytterbium‐centered transition and a residual charge‐transfer emission around 13 150 cm^?1. An efficient antenna effect that proceeds through energy transfer from the singlet excited state of the tetrathiafulvalene‐amido‐2‐pyridine‐N‐oxide chromophore is evidence of the Yb^III sensitization.     

Search for sub-eV mass solar axions by the CERN Axion Solar Telescope with 3He buffer gas

The CERN Axion Solar Telescope (CAST) has extended its search for solar axions by using (3)He as a buffer gas. At T=1.8 K this allows for larger pressure settings and hence sensitivity to higher axion masses than our previous measurements with (4)He. With about 1 h of data taking at each of 252 different pressure settings we have scanned the axion mass range 0.39 eV?m(a)?0.64 eV. From the absence of excess x rays when the magnet was pointing to the Sun we set a typical upper limit on the axion-photon coupling of g(aγ)?2.3×10(-10) GeV(-1) at 95% C.L., the exact value depending on the pressure setting. Kim-Shifman-Vainshtein-Zakharov axions are excluded at the upper end of our mass range, the first time ever for any solar axion search. In the future we will extend our search to m(a)?1.15 eV, comfortably overlapping with cosmological hot dark matter bounds.     

Instability of two-phase flows: A lower bound on the dimension of the global attractor of the Cahn-Hilliard-Navier-Stokes system

We consider a model for the flow of a mixture of two viscous and incompressible fluids in a two or three dimensional channel-like domain. The model consists of the Navier-Stokes equations governing the fluid velocity coupled with a convective Cahn-Hilliard equation for the relative density of atoms of one of the fluids. We prove the instability of certain stationary solutions for such a system endowed with periodic boundary conditions on elongated domains (0,2π/α₀)×(0,2π) or (0,2π/α₀)×(0,2π)×(0,2π/β₀) for a special class of periodic body forces, provided that α₀ and β₀ are small enough. As a consequence, we deduce a lower bound for the Hausdorff dimension of the global attractor.     

On a Regularized Family of Models for Homogeneous Incompressible Two-Phase Flows

We consider a general family of regularized models for incompressible two-phase flows based on the Allen–Cahn formulation in \(n\) -dimensional compact Riemannian manifolds for \(n=2,3\) . The system we consider consists of a regularized family of Navier–Stokes equations (including the Navier–Stokes- \(\alpha \) -like model, the Leray- \(\alpha \) model, the modified Leray- \(\alpha \) model, the simplified Bardina model, the Navier–Stokes–Voight model, and the Navier–Stokes model) for the fluid velocity \(u\) suitably coupled with a convective Allen–Cahn equation for the order (phase) parameter \(\phi \) . We give a unified analysis of the entire three-parameter family of two-phase models using only abstract mapping properties of the principal dissipation and smoothing operators and then use assumptions about the specific form of the parameterizations, leading to specific models, only when necessary to obtain the sharpest results. We establish existence, stability, and regularity results and some results for singular perturbations, which as special cases include the inviscid limit of viscous models and the \(\alpha \rightarrow 0\) limit in \(\alpha \) models. Then we show the existence of a global attractor and exponential attractor for our general model and establish precise conditions under which each trajectory \(\left( u,\phi \right) \) converges to a single equilibrium by means of a Lojasiewicz–Simon inequality. We also derive new results on the existence of global and exponential attractors for the regularized family of Navier–Stokes equations and magnetohydrodynamics models that improve and complement the results of Holst et al. (J Nonlinear Sci 20(5):523–567, 2010). Finally, our analysis is applied to certain regularized Ericksen–Leslie models for the hydrodynamics of liquid crystals in \(n\) -dimensional compact Riemannian manifolds.     

A study of accelerated Newton methods for multiple polynomial roots

We analyze and compare several accelerated Newton methods with built in multiplicity estimates. We also introduce the concept of indicator functions and discuss the Crouse-Putt method. It is shown that many of the accelerated Newton methods not only derive from Schröder’s classic approach but are equivalent. The related computational experiments show that the built in multiplicity estimates can significantly decrease the number of Newton iterations, while the error of these estimates may significantly increase.