Low-temperature EPR study of radical cations of vinyl ethers in a Freon matrix

Using low-temperature EPR the transformations of radical cations of aliphatic vinyl ethers radiolytically generated in a Freon matrix have been investigated. Three-line spectra found at 77 K [hfs constants of 1.5 mT (1H) and 2.2 mT (1H)] and at 95 K [1.9–2.1 mT (2H)] were attributed to the radical cation. A quartet was observed at 130 K, usually with binomial intensities [hfs constants of 1.3 mT (3H)] and a triplet [1.7–1.9 mT (2H)] was found after cooling samples back to 95 K. The conversion of the quartet to the triplet was found to be thermally reversible and both spectra are assigned to different states of a (distonic) dimer cation.     

Self-and cross-phase modulation accompanying third-harmonic generation in a hollow waveguide

The influence of self-and cross-phase modulation on third-harmonic generation in a hollow waveguide is investigated. Analytic solutions of the coupled equations for the slowly varying amplitudes of the pump pulse and the third harmonic in a gas-filled hollow waveguide are obtained with consideration of self-and cross-phase modulation and first-order dispersion effects. The possibility of controlling the nonlinear phase trajectory of the third harmonic by cross-phase modulation is demonstrated. Zh. éksp. Teor. Fiz. 115, 1561–1579 (May 1999)     

Controlling dispersion and transmission spectra of hybrid resonant-gas-filled photonic-crystal optical components

Using the model of an infinite one-dimensional periodic layered structure, we consider the possibilities of controlling dispersion properties and transmission spectra of hybrid optical components consisting of photonic band-gap structures filled with a resonant gas. It is shown that the combination of resonance-enhanced gas dispersion with the dispersion of a photonic band-gap structure may give rise to new features in the dispersion and transmission of hybrid spectral elements. These effects can be employed to create narrowband filters and ultrarefractive prisms with controllable parameters.     

带有阈值转换和启动时间的优先权排队

在诸如ＩＳＤＮ的通信网络中,多种信息共用一条线路,为了满足不同类型信息的服务质量要求,带有阈值转换的优先权排队系统应是一种合适的模型。本文研究单服务员、两类顾客的带有阈值转换和启动时间的优先权排队系统,首先,分别就抢占和非抢占情形讨论了具有泊松到达、服务时间和启动时间均有指数贩系统,然后就非抢占情况进上步考虑了服务时间和启动时间有一般分布的系统,求出了系统中两类顾客队长的稳态联合概率母函数,藉助这     

N‐Propionyl‐1,2‐benzisoselenazol‐3(2H)‐one

The title compound, C₁₀H₉NO₂Se, crystallizes as flat mol­ecules linked by selenium–oxy­gen interactions [Se?O = 3.189 (4) Å] into a linear chain along the a axis of the triclinic cell. The bond dimensions that are derived from ab initio geometry optimization calculations are similar to those determined from the diffraction measurements.     

An anomaly in the magnetic susceptibility of the Mg1−x CuxO solid solutions with 0.01≤x≤0.20

The problem of localized superconductivity has motivated the preparation of Mg_1−x Cu_xO solid solutions with NaCl structure and 0.01≤x≤0.20, as well as a study of the magnetization and magnetic susceptibility χ in the 2–400 K temperature range and in magnetic fields of up to 5 T. The temperature dependence of χ is described for all compositions by the Curie-Weiss law, χ = C/(T − θ), where the constant C is close to the value calculated for each composition for μ_eff = 1.7–1.9μ_B, and θ is close to zero. For T < 30 K, χ(T) deviates for all compositions toward lower χ, which can be attributed to magnetic ordering of exchange-coupled clusters in the solid solution. At T∼320–330 K, an anomaly of a diamagnetic type, i.e., a decrease of χ by 6–30% of its paramagnetic value, has been observed for all compositions against the background of the generally paramagnetic χ(T). A discussion is presented of alternative reasons for this anomaly and of its possible connection with localized superconductivity. __________ Translated from Fizika Tverdogo Tela, Vol. 42, No. 4, 2000, pp. 701–703. Original Russian Text Copyright ? 2000 by Samokhvalov, Arbuzova, Viglin, Naumov, Smolyak, Korolev, Lobachevskaya.     

Solid state electrochemistry, X-ray powder diffraction, magnetic susceptibility, electron spin resonance, Mössbauer and diffuse reflectance spectroscopy of mixed iron(III)-cadmium(II) hexacyanoferrates

Coprecipitates of Cd^II, K^I and Fe^III with hexacyanoferrate ions [Fe(CN)₆]^4? have been studied by solid-state electrochemistry (voltammetry of immobilized microparticles), magnetic susceptibility measurements, X-ray powder diffraction, electron spin resonance, Mössbauer and diffuse reflectance spectroscopy. Most suprisingly, all experimental results point to the formation of a continuous series of complex mixed phases without the formation of phase mixtures. Although Cd^II and Fe^III ions differ too much in their ionic radii to allow the formation of simple substitution mixed hexacyanoferrates, they are capable of forming different kinds of complex insertion and substitution mixed crystals because of the zeolitic structure of both the iron and the cadmium hexacyanoferrate. Low cadmium concentrations can be found in the zeolitic cavities of iron hexacyanoferrate (Prussian blue), and they start to widen the lattice and facilitate, at higher concentrations, the direct substitution of high-spin iron(III) ions by cadmium ions. In cases of an excess of cadmium, the formation of cadmium hexacyanoferrate with iron(III) ions in the interstitials of the zeolitic structure is observed. These mixed phases show strong charge transfer bands in the visible range and have the appearance of “diluted” Prussian blue. For the first time, this indicates that the charge transfer between the carbon-coordinated low-spin iron(II) ions and the high-spin iron(III) ions can also occur when the latter are situated in the cavities of a host hexacyanoferrate. In Prussian blue the interstitial iron(III) ions are responsible for a very strong charge transfer interaction between the low-spin iron(II) ions and the nitrogen-coordinated high-spin iron(III) ions. Upon substitution of the very small amount of interstitial iron(III) ions in Prussian blue by potassium and cadmium ions the Kubelka-Munk function diminishes by more than 30%, indicating a tremendous decrease in iron(III)-iron(II) interaction.     

Two-dimensional incommensurate superlattices in precious-metals alloys: Nature of formation

The nature of two-dimensional incommensurate superlattices Ll₂ (MM) obtained in the precious-metals alloys Au₃ Cu and Cu₃ Pd is investigated on the basis of first-principles calculations of the electronic structure. It is shown that their stability can be explained by the opening of energy gaps on coinciding sections of the Fermi surface in two mutually perpendicular directions. It is important that this explanation holds only if the superlattice is treated as a superstructure with respect to ordinary superstructures (Ll₂): the electronic spectrum of the superstructure and not the disordered alloy (as in the existing electronic theory of one-dimensional long-period structures) should serve as the starting spectrum. Arguments supporting the fact that in a number of quasicrystal-line substances the Ll₂ (MM) phases fall between incommensurate systems and quasicrystals are presented. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 8, 548–554 (25 April 1999)     

The Elusive Structure of Levocetirizine Dihydrochloride Determined by Electron Diffraction

Levocetirizine is an orally administrated, second-generation antihistaminic active pharmaceutical ingredient that has been used to treat symptoms of allergy and long-term hives for over 25 years. Despite the wide use of this compound, its crystal structure has remained unknown. Here we report the application of 3D electron diffraction (3D ED)/Micro-crystal electron diffraction (MicroED) to determine the crystal structure of Levocetirizine dihydrochloride directly from crystalline powders that were extracted from commercially available tablets containing the compound. We also showcase the utility of dynamical refinement to unambiguously assign absolute configuration. The results highlight the immense potential of 3D ED/MicroED for structure elucidation of components of microcrystalline mixtures that obviates the need to grow large-size single crystals and the use of complementary analytical techniques, which could be important for identification as well as for primary structural characterization.