Panchromatic Chromophore Mixtures in an AlPO4‐5 Molecular Sieve: Spatial Separation Effects and Energy Transfer Cascades

Dye‐loaded AlPO₄‐5 single crystals were prepared by microwave‐assisted hydrothermal synthesis from a batch, containing a mixture of three chromophores (Coumarin 40, Rhodamine BE50, and Oxazine 1) differing in their absorption range, molecular dimensions, and solubilities. Confocal fluorescence images reveal a spatial separation effect of the dye molecules, where the slimmer, more‐soluble dye molecule (Coumarin 40) is uniformly distributed in the body of the single crystal, and the bulky and/or less‐soluble ones (Rhodamine BE50, Oxazine 1) are situated in distinct domains. Visible spectra show good panchromatic absorption of visible light. Fluorescence lifetime measurements indicate the presence of an energy transfer cascade of the entirely fixed dye molecules from Coumarin 40 to Oxazine 1. The transfer mechanism is predominantly radiative.     

Photosensitivity of surface barrier structures based on Cu(In,Ga)Se<Subscript>2</Subscript> films grown by codeposition in vacuum

Polycrystalline Cu(In,Ga)Se₂ (CIGS) films with various ratios of Cu, In, and Ga were grown by codeposition of all elements in vacuum. The X-ray diffraction study showed that the films are single-phase and possess a chalcopyrite structure with predominant [112] orientation. The films exhibited a mirror smooth surface and had a close-packed structure composed of crystallites with clear faceting and a transverse size of 0.1–0.3 μm. Related surface barrier structures of the (In,Ag)/Cu(In,Ga)Se₂ type were obtained and their spectra of the quantum efficiency of photoconversion were studied. The obtained structures can be used for optimization of the CIGS film technology.     

Synthesis and Study of Alkaline-Earth Metal Uranoborates,AI I(BUO5)2·nH2O

Previously unknown compounds A^{I I}(BUO₅)₂·nH₂O (A^{I I} = Mg, Ca, Sr, Ba; n = 0-7) were synthesized. Their structure and thermal decomposition were studied by X-ray diffraction, IR spectroscopy, and thermal analysis.     

Thermal conductivity of doped PbTe-based solid solutions with off-center impurities

The coefficients of thermopower and electrical and thermal conductivity in the PbTe_0.8Se_0.1 S _0.1 solid solution with electron concentration (4.6–54) × 10¹⁸ cm^?3 are studied in the range of 85–300 K (and in some cases up to 700 K). The temperature dependences of electrical and thermal conductivity indicate that the low-temperature electron and phonon scattering initiated by the off-center impurity of sulfur exists. The temperature dependences of the electronic and lattice components of thermal conductivity are calculated in the approximation of a parabolic spectrum and electron scattering by acoustic phonons and neutral substitutional impurities. The lattice thermal conductivity is found to have a feature in the form of a shallow minimum in the range of 85–250 K. A similar feature, while not so clearly pronounced, is found to exist also in Pb_1?x Sn_xTe_1?x Se_x alloys (x≥0.15) with an off-center tin impurity. An analysis of the possible origins of this effect suggests that, at low temperatures, the Lorentz numbers L of the materials under study are smaller than the L₀ numbers employed which correspond to the above scattering mechanisms. The cause of the decrease in L is related to electron scattering at two-level systems, a mechanism whose effect grows with increasing electron energy. An analysis of experimental data obtained at high temperatures, as well as on undoped samples with the lowest possible carrier concentrations, yields the values of L for samples with different electron densities. The minimum value L/L₀ = 0.75 is obtained for a lightly doped sample at ～130 K.     

A left-handed composite medium based on waveguiding structures with a bianisotropic filling

A new composite medium based on waveguiding structures loaded with bianisotropic gratings of planar double split rings (PDSRs) and planar helices is considered. The microwave transmission spectra of this medium are studied experimentally. The effective parameters of the medium are determined theoretically, and its passbands are investigated. The characteristics of the medium are compared to those of infinite homogeneous bianisotropic media. A relationship between the spectral transmission characteristics and the type of resonance excitation is established. The transparency bands and overforbidden bands of the composite medium are revealed. The combinations of the medium’s effective parameters that correspond to these bands are determined. It is shown that the transparency bands where the medium is characterized simultaneously by negative permittivity and negative permeability can be identified.     

Nondiffusive weak localization in two-dimensional systems with spin-orbit splitting of the spectrum

The effect of spin splitting caused by structural asymmetry (Rashba’s contribution) and bulk asymmetry (Dresselhaus’s contribution) on the magnetoconductance of two-dimensional structures with high mobility of charge carriers is studied. The theory of weak localization with regard to both of the contributions is developed. The theory is valid in the entire region of classically low magnetic fields for arbitrary relations between the frequencies of spin precession and elastic collisions. The suppression of the correction for antilocalization is demonstrated in the case of equal contributions of structural anisotropy and bulk anisotropy to the spin splitting. The effect of the contribution, cubic in the wave vector, to the spin splitting on the quantum magnetoresistance is studied.     

Electrical and photoelectric properties of electrochemically fabricated SnO2/Cd0.4Zn0.6S/CdTe solar cells

Solar cells based on SnO₂/Cd_0.4Zn_0.6S/CdTe heterostructures are fabricated by electrochemical deposition, and the dependences of their electrical and photoelectric properties on the thermal annealing conditions are studied. It is shown that thermal annealing reduces the tunnel currents by almost two orders of magnitude. The best conditions of thermal annealing are determined (t = 300°C and τ = 9 min). These conditions provide the highest photosensitivity of the heterostructures under study (I _sc ≈ 21.2 mA/cm², U _oc ≈ 813 mV, and η = 14.7%).     

Equivalent electrical network of the DNA molecule

The variation of current density with bias or temperature is examined for DNA molecules of different configuration. To this end, the DNA molecule is represented as an equivalent electrical network whose behavior is then simulated with PSPICE. The results are found to be in close agreement with ones obtained within a physical model. It is established that the electrical response of a DNA molecule to an applied electric field depends on the boundary conditions and the potential profile along the molecule. This finding should contribute to the creation of a complete library of DNA-molecule configurations with prescribed electrical properties.     

Dynamics of liquid-filled spacecraft

A method is presented for simulating coupled liquid-solid dynamics. An important example of a coupled liquid-solid system is a satellite carrying fuel. The dynamics of the satellite and the onboard fuel influence each other, which may lead to satellite motion that is uncontrollable. For better understanding of the complex dynamics of coupled systems, a numerical model is developed. The model consists of two parts. The first part that solves the liquid motion is only briefly discussed here. The focus in this paper is on the way in which the dynamics of the liquid and the solid body are coupled. For this, the governing equations are presented in which terms appear that represent the force and torque on the solid body due to the sloshing liquid. The governing equations are rewritten such that the discrete approximation of these equations can be integrated in a stable manner for arbitrary liquid/solid mass ratios. Results are presented demonstrating the stability of the present model. A grid-refinement study and a time-step analysis are performed. Finally, the flat-spin motion of a satellite, partially filled with liquid, that flew in 1992 as part of the Wet Satellite Model experiment is studied. Results from the simulation are compared with the actual flight data.     

Self-oscillating dimmable electronic ballast

This paper presents a simple alternative for an electronic ballast operating in self-sustained oscillating mode with dimming capability for fluorescent lamps. A simple modification in one of the gate drivers side circuit allows the lamp to dim without compromising the simplicity, reliability, and low cost which characterize the self-oscillating electronic ballast (SOEB). A qualitative analysis is presented to explain the behavior of the proposed self-oscillating electronic ballast with dimming feature. In addition, the stability and the key equations for the design are derived using the extended Nyquist criterion and describing function method. Experimental results from two 40-W electronic ballasts are presented to demonstrate the performance and to validate the analysis carried out.