Fluorescence resonance energy transfer in a non-conjugated system of CdSe quantum dots/zinc-phthalocyanine

Energy transfer between CdSe quantum dots (QDs) as donors and Zn phthalocyanine (Zn-Pc) molecules as acceptors was studied using steady-state photoluminescence and time-correlated single photon counting techniques. With the latter technique it is evaluated that the lifetime of Zn-Pc emission increases from 4 ns to ca. 30 ns on 460 nm excitation in the presence of the QDs. The concomitant decrease in the lifetime of the QDs emission (from 23.5 to 18.4 ns) indicates that the excitation of Zn-Pc occurs not only through reabsorption but also through fluorescence resonance energy transfer.     

Materials processing with a tightly focused femtosecond laser vortex pulse

In this Letter we present the first (to our knowledge) demonstration of material modification using tightly focused single femtosecond laser vortex pulses. Double-charge femtosecond vortices were synthesized with a polarization-singularity beam converter based on light propagation in a uniaxial anisotropic medium and then focused using moderate- and high-NA optics (viz., NA=0.45 and 0.9) to ablate fused silica and soda-lime glass. By controlling the pulse energy, we consistently machine micrometer-size ring-shaped structures with <100nm uniform groove thickness.     

Synthesis of 4‐Substituted Piperidines via a Mild and Scalable Two‐Step Cu2O‐Mediated Decarboxylation of Cyanoesters

A four‐step, high‐yielding, kilogram‐scale protocol to prepare aldehyde 5 is reported. The key reaction is a mild, two‐step Cu₂O‐mediated decarboxylation of cyanoester 3 that proceeds in excellent yield. The general applicability of this methodology has also been explored.     

Phenyl-cyclohexyl enaminoketone ligands and their Cu(II) complexes

The liquid crystalline properties of 1-(alkylamino)-3-[(4'-hexyl-trans-cyclohexyl-4'-phenyl]-prop-1-en-3-one-s, from methyl to octadecyl, and their copper (II) complexes have been examined by optical, DSC, X-ray and EPR methods. The compounds are enantiotropic nematogens except those having the shortest and the longest terminal chains. Short chains promote the S_A phase in both ligands and complexes, whereas long chains promote S_C and crystal H phases for the ligands or S_A and S_C phases for the complexes. A partly bilayer smectic A_d phase is observed from ligands terminated with short non-polar substituents. Direct isotropisation from the crystal H phase for some of the compounds, as well as other phase transitions have been studied. The molecular shape of the complexes and the organization of their mesomorphic phases are discussed, based on the refractive indices and X-ray data.     

Phenolic constituents of Knautia arvensis aerial parts

A new C-6 flavone glycoside (6), together with seven known compounds, cryptochlorogenic acid (1), chlorogenic acid (2), 2-O-trans-caffeoylhydrocitric acid (3), isovitexin 7-beta-D-glucopyranoside (4), 7,4'-dihydroxy-5-methoxyflavone-6-C-beta-D-glucopyranoside (5), 3,5-O-dicaffeoylquinic acid (7) and 4,5-O-dicaffeoylquinic acid (8), were isolated from the aerial parts of Knautia arvensis. Their structures were elucidated by extensive spectroscopic methods including 1D- (1H, 13C and TOCSY) and 2D-NMR (DQF-COSY, HSQC, HMBC) experiments, as well as ESIMS analysis. Compounds 1, 3-5 and 8 are reported for the first time in Knautia arvensis.     

Entropic derivation of the spectral Eddington factors

In general, the closure of the finite system of moment equations by the corresponding maximum entropy distribution function results in the symmetric conservative system of first-order partial differential equations for the Lagrange multipliers of the constrained Boltzmann entropy maximization problem. Then the transformation of dependent variables yields the system of conservation equations for the moments which is consistent with the additional conservation equation identified with the balance of entropy. The objective of this paper is to employ these facts for the analysis of the spectral Eddington factors obtained from the maximum entropy distribution functions. The supposition that the spectral Eddington factors should depend on the energy density and the heat flux only through the single variable representing the heat flux normalized in some way by the energy density predominates in the literature on the subject. Here, it is demonstrated that this is true only for classical Maxwell-Boltzmann radiation and, in this case, the well-known results of Minerbo are recovered. A similar single-variable dependence postulated by Cernohorsky and Bludman for fermionic radiation cannot be justified since it leads to the contradiction with the consistency conditions between the moment evolution equations and the entropy balance. For Bose-Einstein radiation, we rederive and analyze the results given in the literature for low-energy and high-energy limits. We also show that, except for those limiting cases, the Eddington factor for bosonic radiation cannot be represented as a function of a single normalized variable. In the present approach, the entropy function plays a crucial role in determining the system of evolution equations for the energy density and the heat flux. In this system, the flux of the heat flux, and hence the Eddington factor, is determined by the additional scalar potential uniquely related to the entropy function for each type of statistics. Since the Eddington factor cannot be expressed in terms of elementary functions, we propose to use the polynomial approximation. Namely, for Maxwell-Boltzmann, Fermi-Dirac, and Bose-Einstein statistics, we expand the entropy function in powers of the square of the heat flux and also calculate the corresponding power series expansion of the additional potential. By truncating the latter, we obtain the Eddington factor represented as the eighth-order polynomial in the heat flux with coefficients being the elementary functions of the energy density and the parameter which determines statistics. Finally, we analyze the behavior of the scalar Eddington factors in the limiting case when the normalized heat flux tends to one.     

Tailoring Čerenkov second-harmonic generation in bulk nonlinear photonic crystal

We investigate theoretically the ?erenkov-type second-harmonic generation in two-dimensional bulk nonlinear photonic crystal with longitudinal modulation of the χ((2)) nonlinearity. We show that in this scheme the ?erenkov radiation can be achieved simultaneously at multiple directions with comparable intensities. The angles of emission are controllable by the spatial modulation of the nonlinearity. We propose a design of the periodically poled domain pattern, which maximizes the efficiency of the second-harmonic emission.     

Third-harmonic generation via nonlinear Raman-Nath diffraction in nonlinear photonic crystal

We report on the observation of multiple third-harmonic conical waves generated in an annular periodically poled nonlinear photonic crystal. We show that the conical beams are formed as a result of the cascading effect involving two parametric processes that satisfy either the transverse and/or longitudinal phase-patching conditions. This is the first experimental observation of third-harmonic generation based on nonlinear Raman-Nath diffraction.     

Congruences on Menger algebras

We discuss some types of congruences on Menger algebras of rank n, which are generalizations of the principal left and right congruences on semigroups. We also study congruences admitting various types of cancellations and describe their relationship with strong subsets.     

A Generalization of n-Ary Algebraic Systems

One of the aims of this article is to extract, whenever possible, the common elements of several seemingly different types of algebraic hypersystems. In achieving this, one discovers general concepts, constructions, and results which not only generalize and unify the known special situations, thus leading to an economy of presentation, but, being at a higher level of abstraction, can also be applied to entirely new situations, yielding significant information and giving rise to new directions. We shall consider a class of algebraic hypersystems which represent a generalization of semigroups, hypersemigroups, and n-ary semigroups. This new class of hypersystems is called n-ary hypersemigroups and properties of such hypersemigroups are investigated. On an n-ary hypersemigroup, we describe the smallest equivalence relation β* whose quotient is an ordinary n-ary semigroup.