Optimization of the Ambulance Fleet Location and Relocation

Journal of Applied and Industrial Mathematics - We study the problem of optimal location of the ambulance fleet at the base stations. The objective is to minimize the average waiting time for...     

Electric field selectivity and multiplexing of volume holograms in LiNbO3

Theoretical and experimental investigations of electric field multiplexing and selectivity of reflection volume holograms in LiNbO₃ are reported. Recording of at least five holograms is demonstrated. Equivalent spectral selectivity (5Ƽ.5 pm for the case of three electrically tunable holograms and (5ǁ pm for the case of five electrically tunable holograms are estimated.     

Orientational dependencies of space-charge waves under the action of a magnetic field in GaAs:Cr

Space-charge wave (SCW) excitation is studied under the influence of an external magnetic field in GaAs:Cr depending on the orientational angle of the exciting oscillating sinusoidal interference pattern to the external electric field. It was found that the tilt of the SCW propagation direction induced by the magnetic field results in a shift of the orientational dependence curve. This feature allows determining the deviation angle of charge carriers’ trajectory and their sign. A quantitative theoretical explanation of the effects is proposed and a theoretical expression for the SCW ac-current is given.     

Crystal structure and superconductivity of Bi-2223

The crystal structure of the Bi₂Sr₂Ca₂Cu₃O_{10 + x} high-temperature superconductor is investigated by the X-ray Rietveld method. The results obtained are used to analyze the structural features of the bismuth high-temperature superconductors in respect to their superconducting properties. The refinement of the structure of the Bi-2223 compound in the four-dimensional space group A2aa (a00) 000 (Z = 4) with the vector q ～ 0.21a* does not reveal any indication of a modulated structure of the Bi-2212 type. The lattice parameters are 5.411(3), 5.409(1), and 37.082(1) Å. The agreement factors are R _wp = 8.10% and R _p = 5.49%. The results obtained are consistent with the notion that bismuth high-temperature superconductors are supercon-ductors with a more distorted crystal structure as compared to other representatives of high-temperature superconductors with critical temperatures T _c > 100 K. These distortions primarily manifest themselves in the segregation of the Bi and O ions of the “charge block” with the formation of zigzag chains that are characteristic of the structure of Bi₂O₃ and are stimulated in particular by defects in the calcium layer.     

Effects of resistance switching in niobium oxides: Metastable nanochannels

The recent experimental data suggest that lattice defects in transition-metal oxides tend to be aligned into chains, which can promote pairing of charge carriers with subsequent formation of bosonic stripes. In this study, possible relationship between the extraordinary manifestations of electronic properties, observed by different methods in niobium oxides, and the processes of formation of metastable nanochannels from bosonic stripes are discussed.     

Electrically controlled slow/fast propagation of 12.5-GHz light pulses in lithium niobate waveguide Bragg grating

Experiments on slow/fast light propagation in the Bragg grating recorded in the optical waveguide formed in a photorefractive copper-doped lithium niobate wafer are reported. The change from slow to fast light propagation in the 8-mm-long grating with spectral FWHM of ≈0.14 nm and maximum Bragg reflection of ≈90% was achieved by tuning the carrier wavelength around the central Bragg value of ≈1553.36 nm. Effective electrooptical control of the 80-ps pulse shift (fractional delay/advancement of up to 0.4) was demonstrated by applying an external voltage of ≈80 V to the electrodes deposited on the waveguide sides.     

Texture of Y- and Bi-HTSC and Methods for its Determination

Investigation of the texture of Y- and Bi-HTSC materials by X-ray techniques involves certain difficulties owing to the peculiarities of their crystal structure which causes the arrangement of reflexes in dense groups and practically precludes the formation of a pole figure from an isolated reflex. The texture of Y- and Bi-HTSC materials has been investigated by constructing direct pole figures in an automatic texture diffractometer DAPT YM 1 in CuKα emission from groups of reflexes which are unresolvable under the test conditions. The choice of groups of reflexes was dictated by the type of texture formed. With a basal texture of packing of powders, the following groups have turned out to be the most suitable for the YBa₂Cu₃O_7–x phase (123): (013) + (110) + (103), 2θ = 32.3 – 32.8º and (014) + (005) + (104), 2θ = 38.5 – 38.8º. They include the reflexes which are structural and superstructural relative to a bcc subcell with a rather slight orthorhombic distortion, with its tripling along the “c” axis forming a cell of (123) compound. For the Bi₂Sr₂CaCu₂O₈ phase, there have been used the groups of reflexes (008) + (111) + (1.4/54), (0.0.10) + (1.6/5.4) + (0.9/5.1), (0.0.12) + (1.6/5.8) + (204) + (119). (115) + (1.6/5.4) + (0.1/5.9), and (117) + (0.9/5.1) + (1.6/5.6) + (1.4/5.8), 2θ with respectively 23.2 – 24.0º, 29.1 – 29.7º, 35.1 – 35.2º, 36.5 – 28.4º, and 29.7 – 31.4º. They also include reflexes from the lattice constructed by multiplication of a perovskite cell with α = 5.40 Å, b = 5.41 Å and c = 30.6 Å along the “b” axis. Y-HTSC-based materials also contain a component of shear texture which is close to such a texture in bcc metals. The texture of Y- and Bi-HTSC materials is relatively stable in hightemperature annealing. The nature of the effect of annealing at moderate temperature is different.