Structural studies of AgSbTe2 under pressure: Experimental and theoretical analyses

The crystal structure of AgSbTe₂ has been refined using first-principles calculations, from which the ordering of the cations, Ag and Sb, was confirmed. The spontaneous formation of two (D4 and L1₁) phases at ambient and elevated pressure was demonstrated theoretically. The compound was also prepared and its high-pressure structural deformation sequence, ranging from ambient to 50.9 GPa, was observed with synchrotron radiation at room temperature. The compound underwent a pressure-induced amorphization (PIA) at 24.6 GPa and then started recrystallizing at 49.2 GPa. The bulk modulus (B₀) and pressure derivative of the bulk modulus (B_p) were determined experimentally to be 56.3 ± 5.1 GPa and 4.3 ± 0.8, respectively. We suggest that large displacements of Te atoms to Ag vacancy positions are responsible for PIA and the recrystallization.     

First measurement of inclusive B→Xsη decays

We report a first measurement of inclusive B→Xsη decays, where Xs is a charmless state with unit strangeness. The measurement is based on a pseudoinclusive reconstruction technique and uses a sample of 657×10(6)BB pairs accumulated with the Belle detector at the KEKB e+e- collider. For MXs < 2.6 GeV/c2, we measure a branching fraction of [26.1±3.0(stat)-2.1+1.9(syst)-7.1+4.0(model)]×10(-5) and a direct CP asymmetry of ACP=-0.13±0.04-0.03+0.02. Over half of the signal occurs in the range MXs > 1.8 GeV/c2.     

Laser-induced acoustic wave generation/propagation/interaction in water in various internal channels

Short pulsed laser-induced single acoustic wave generation, propagation, interaction within a water-filled internal channel are experimentally and numerically studied. A large-area, short-duration, single-plane acoustic wave was generated by the thermoelastic interaction of a homogenized nanosecond pulsed laser beam with a liquid–solid interface and propagated at the speed of sound in water. Laser flash Schlieren photography was used to visualize the transient interaction of the plane acoustic wave in various internal channel structures ((a) sudden expansion and contraction channels, (b) bifurcating channels, (c) gradual contraction wall channels and (d) a cylinder). Fairly good agreement between the experimental results and numerical simulation is observed.     

The effect of substrate heating on the tunability of rf-sputtered Bi2O3-ZnO-Nb2O5 thin films

Reactively rf-sputtered Bi₂O₃-ZnO-Nb₂O₅ (BZN) thin films were prepared on Pt(111)/TiO₂/SiO₂/Si with substrate heating. The effects of substrate heating on the structures, morphologies, dielectric properties, and voltage-tunable dielectric properties of the films were investigated. With heating, the BZN thin films could be deposited in crystalline form as the cubic pyrochlore phase. The amounts of secondary phases, such as zinc niobate and bismuth niobate, depended on the substrate temperature. The more compounding of the BZN crystalline phase proceeded at deposition, the less formation of secondary phases and stoichiometric change occurred after post-annealing. Therefore, improvement of the dielectric constant and tunability of thin films by grain-size enlargement might be possible with proper substrate heating and post-annealing. The BZN thin films sputtered with a substrate temperature of 550 °C and annealed at 800 °C showed a maximum tunability of 26.5% at a dc bias field of 1000 kV/cm and measurement frequency of 1 MHz. PACS 81.15.Cd; 77.55.+f; 77.84.Dy; 81.40.Tv     

Experimental evidence of chiral crown ether complexation with aromatic amino acids

The complexation of L ‐ and D ‐enantiomers of phenylglycine, phenylalanine, and tryptophan with D ‐mannonaphto‐crown‐6‐ether in methanol solution was studied by NMR and isothermal titration calorimetry (ITC) at 298.15 K. The total heat effects attributed to the binding phenomena were measured in the range of 1.8 to 7.7 mJ, and the complexation was found stereo‐specific. The binding topologies were estimated basing on ¹H 2D‐ROESY experiments. The analysis of Job plots obtained from ¹H NMR‐monitored titrations proved the coexistence of 1:1 and 1:2 (crown ether:amino acids) complexes, which thermodynamic parameters, K_s, ΔG, ΔH°, and TΔS were determined with the aid of ITC. The 1:1 complexes were found enthalpically stabilized, generally by electrostatic interactions between the charged NH group of amino acid and crown ether macrocyclic moiety, while the binding of the second amino acid molecule was driven entropically due to solvatophobic effect. Strong enthalpy–entropy compensation points towards the uniform binding mode of all complexes studied. The mode of complex formation was found solvent dependent. For phenylalanine guest studied in various solvent systems, in contrast to the aqueous media, the noticeable chiral recognition is observed in methanol solution, and the complex stoichiometry (1:2 ether:Phe) differs from the 2:1 one, determined previously for the same host‐guest system in water (J. Thermal. Anal. Cal. 2006; 83: 575–578). Copyright © 2007 John Wiley & Sons, Ltd.     

Optical absorption of 1-phenyl-3-methyl-1H-pyrazolo[3,4-b]quinoline derivatives: Molecular dynamics modeling

Paper deals with quantum chemical modeling of the optical absorption spectra of 6-fluoro, 7-trifluoromethyl, 6-cyano, 6-carboethoxy and 6-tert-butyl derivatives of 1-phenyl-3-methyl-1H-pyrazolo[3,4-b]quinoline. The calculations are performed by means of the semiempirical quantum chemical methods (AM1 or PM3) applied to the equilibrium molecular conformation in vacuo (T = 0 K) or molecular dynamic (MD) trajectories as obtained within fragmental or total MD simulations at T = 300 K. The results of these calculations are compared with the measured spectra of optical absorption. The quantum chemical analysis show that the dynamics of the methyl, trifluoromethyl, carboethoxy and tert-butyl groups practically does not influence the absorption spectra whereas the strongest their modifications are found to be related with dynamics of the aromatic group. The semiempirical method AM1 in combination with MD simulations gives for all dyes the best agreement between the calculated and measured spectral positions of absorption bands. In most cases the quantum chemical calculations describe properly the trends of their changes depending on the lateral substituent.     

Ultrahigh-resolution optical coherence tomography using continuum generation in an air-silica microstructure optical fiber

We demonstrate ultrahigh-resolution optical coherence tomography (OCT) using continuum generation in an air-silica microstructure fiber as a low-coherence light source. A broadband OCT system was developed and imaging was performed with a bandwidth of 370 nm at a 1.3-mu;m center wavelength. Longitudinal resolutions of 2.5 microm in air and ~2 microm in tissue were achieved. Ultrahigh-resolution imaging in biological tissue in vivo was demonstrated.     

Two-electron entanglement in elliptically deformed quantum dots

Entropic entanglement measures of a two-dimensional system of two Coulombically interacting particles confined in an anisotropic harmonic potential are discussed in dependence on the anisotropy and the interaction strength. The harmonic approximation appears exact in the strong interaction limit, allowing determination of the asymptotic expression for the linear entropy. Entanglement properties are dramatically influenced by the anisotropy of the confining potential in the strong-correlation regime.     

Hybrid Plasma – Prospects for Application in Medicine and Biology

Russian Physics Journal - Different schemes and designs of generators of low-temperature hybrid plasma produced by simultaneous ionization of plasma-generating medium by an electron beam with...     

Intensity measurements in the v4-fundamental of methane

The absolute intensities of all the J-multiplets between R(13) at 1375cm^-1 and P(12) at 1225 cm^-1, in the v₄-fundamental of ¹²CH₄, have been measured at 300°K. Our values are consistent with published band-intensity measurements and also with the theoretical line strength tabulation by Fox. Spectral transmittance computation using a Lorentz line shape with a hydrogen-broadened half-width of 0.075 cm^-1 atm^-1 at 300°K for all the lines in the band is in excellent agreement with our experimental data measured with a spectral resolution of 0.2 cm^-1. Our best estimate for the absolute intensity of the band is 145±8 cm^-2 atm^-1 at STP.