Surface structure of magnetite (111) under hydrated conditions by crystal truncation rod diffraction

X-ray crystal truncation rod (CTR) diffraction under hydrated conditions at circum-neutral pH was used to determine the surface structure of Fe₃O₄(111) following a wet chemical mechanical polishing (CMP) preparation method. The best-fit model to the CTR data shows the presence of two oxygen terminated domains that are chemically inequivalent and symmetrically distinct in the surface contribution ratio of 75% oxygen octahedral-iron (OOI) termination (^aO_2.61–^aO_1.00–^oh1Fe_2.55–^bO_1.00–^bO_3.00–^td1Fe_1.00–^oh2Fe_1.00–^td2Fe_1.00–R) to 25% oxygen mixed-iron (OMI) termination (^bO_1.00–^bO_3.00–^td1Fe₀–^oh2Fe_1.00–^td2Fe_1.00–^aO_3.00–^aO_1.00–^oh1Fe_3.00–R). An adsorbed water layer could not be constrained in the best-fit model. However, bond-valence analyses suggest that both of the surfaces are hydro-oxo terminated. Furthermore, the topmost iron layers of both domains are inferred to be occupied with the redox active Fe²⁺ and Fe³⁺ cations indicating that these irons are the principle irons involved in controlling the surface reactivity of magnetite in industrial and environmentally relevant conditions.     

Ultrasonic concentration measurement of aqueous solutions using PLS regression

This work demonstrates the use of a multivariate statistical technique called partial least squares (PLS) to extract material related data by analyzing spectra of ultrasonic pulses. We show how PLS can be used to estimate the concentration of sodium chloride in an aqueous solution. The paper describes the use of PLS and discusses pre-processing of ultrasonic data, the PLS algorithm as well as model validation. The measured concentrations are compared to reference values. The influence of disturbances and parameter changes is highlighted. The proposed method is easily adaptable to similar applications and permits a cost-saving implementation using existing and approved hardware.     

Particle image velocimetry: Estimation of measurement confidence at low seeding densities

In order to optimise the spatial resolution of particle image velocimetry, it is often necessary to take measurements from regions of the photographic record which contain few particle images. If Young's fringe analysis is used in these cases, the observed fringe pattern is confused by extraneous spatial frequency components or speckle noise. If spatial correlation analysis is employed, spurious correlation peaks occur. In this paper we introduce a definition of signal to noise ratio appropriate to particle image velocimetry and investigate the statistical variation of this ratio as a function of the seeding particle size and concentration.     

The wettability of poly(tetrafluoroethylene) by aqueous solutions of ternary surfactant mixtures

Contact angle measurements on poly(tetrafluoroethylene) (PTFE) surface were carried out for the systems containing ternary mixtures of cetyltrimethylammonium bromide (CTAB) and p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycols), Triton X-100 (TX100) and Triton X-165 (TX165). The aqueous solution of ternary surfactant mixtures were prepared by adding the third surfactant to the binary mixture of the surfactants where the synergetic effect in the reduction of the surface tension of water was determined, to compare the influence of the third surfactants on the values of surface tension of this binary mixture and the values of the contact angle on PTFE. The obtained results and calculations indicate that the ternary mixtures of CTAB + TX165 (αCTAB = 0.2, γ_LV = 60 and 50 mN/m) + TX100 (C = 10⁻⁸ to 10⁻² M) have the biggest efficiency of the reduction of contact angle of water on PTFE in comparison to aqueous solutions of the single surfactants and their binary and ternary mixtures. Also in the case of all studied ternary mixtures of surfactants at concentrations of the bulk phase corresponding to unsaturated monolayer at water-air interface the adsorption of surfactants at PTFE-water interface is different than that at water-air interface, but is the same at concentrations near the critical micelle concentration (CMC). Thus the linear dependences between γ_LV cos θ − γ_LV and cos θ − 1/γ_LV, in the range of concentration studied for all systems confirm the same adsorption at two interfaces only at C near the CMC.     

Radiation chemistry of tris(acetylacetonato) cobalt(iii) in aqueous solutions

Abstract

On radiolysis tris(acetylacetonato) cobalt(III) in aqueous solutions is found to get reduced by reaction with (1) hydrated electrons, (2) H atoms, (3) OH radicals and (4) C₂H₂OH radicals. The bimolecular rate constants for the first three reactions, determined by competition kinetics are: 4 × 10¹⁰, 2.3 × 10⁹ and 4.7 × 10⁹ M^?1sec^?1 respectively. Absorption spectra of the irradiated solutions indicate the formation of bis(acetylacetonato) cobalt(II) from reaction (1), but not from (3). The total cobaltous yield in air-free solutions is given byG(Co⁺⁺) = 5.6 and 6.5 at pH 6.5 and 1 respectively. It appears that G_eaq- ∽ _H ⁺ G_oH ∽ 2.8 in neutral solutions. Considerations of material balance for the primary yields of radiolysis of water suggest the possibility that the so-called independent H-atoms in neutral solutions are probably excited water molecules or ion-pairs.     

A simplified SO(6,2) model of SU(3)

A new realization is obtained of the representation of so(6,2) which has been shown recently by Flath and Biedenharn, and also by Bracken and MacGibbon, to define a model of SU(3). In contrast to the realization in terms of six pairs of boson operators used previously, which involved cubic expressions, the new realization involves only quadratic expressions in eight pairs of boson operators, and is manifestly hermitian. Properties of this new oscillator realization, and in particular its advantages over the old realization, are discussed briefly. It is deduced that the representation of so(6,2) is integrable to a unitary group representation.On leave from Department of Mathematics, University of Queensland, Australia     

Photonic crystal fiber based evanescent-wave sensor for detection of biomolecules in aqueous solutions

We demonstrate highly efficient evanescent-wave detection of fluorophore-labeled biomolecules in aqueous solutions positioned in the air holes of the microstructured part of a photonic crystal fiber. The air-suspended silica structures located between three neighboring air holes in the cladding crystal guide light with a large fraction of the optical field penetrating into the sample even at wavelengths in the visible range. An effective interaction length of several centimeters is obtained when a sample volume of less than 1 microL is used.     

Association of Zn(II)tetra-4-carboxyphthalocyanine in aqueous solutions

Association of Zn(II)tetra-4-carboxyphthalocyanine in aqueous solutions is studied. The influence of the permittivity of the solvent and pH of the medium and the effects of adding ethanol, electrolytes, electron donor materials, and π-π complexing agents on the state of Zn(II)tetra-4-carboxyphthalocyanine in a solution are revealed.     

Electron paramagnetic relaxation in aqueous solutions of manganese (II) ions

The processes of the electron paramagnetic relaxation, molecular motions and structural changes in aqueous solutions of manganese nitrate have been investigated by direct measurement of spin-lattice (T ₁) and spin-spin (T ₂) relaxation times for a wide range of concentrations, temperatures and viscosities. T ₁ and T ₂ were measured by a non-resonance absorption method.

It was discovered that some structural regions exist at the different concentrations of Mn(II) ions in solution. So, the structure of highly concentrated solutions may be considered as one of the corresponding crystallohydrate. The structural microinhomogeneities were observed also in the intermediate concentration range at definite temperatures. It is shown that the relaxation mechanism proposed by Bloembergen and Morgan is not effective in the concentration range studied by us.

The analysis of relaxation times and E.P.R. spectra has shown the formation of ‘liquid microphases’ at the freezing point of the solution. Such microphases can exist at temperatures a few tenths of a degree below the solvent freezing point, and its composition considerably differs from the initial solution.

The correlation times for intramolecular and intermolecular electron relaxation mechanisms are evaluated and their nature is discussed.     

Consequences of (129)Xe-(1)H cross relaxation in aqueous solutions.

We have investigated the transfer of polarization from (129)Xe to solute protons in aqueous solutions to determine the feasibility of using hyperpolarized xenon to enhance (1)H sensitivity in aqueous systems at or near room temperatures. Several solutes, each of different molecular weight, were dissolved in deuterium oxide and although large xenon polarizations were created, no significant proton signal enhancement was detected in l-tyrosine, alpha-cyclodextrin, beta-cyclodextrin, apomyoglobin, or myoglobin. Solute-induced enhancement of the (129)Xe spin-lattice relaxation rate was observed and depended on the size and structure of the solute molecule. The significant increase of the apparent spin-lattice relaxation rate of the solution phase (129)Xe by alpha-cyclodextrin and apomyoglobin indicates efficient cross relaxation. The slow relaxation of xenon in beta-cyclodextrin and l-tyrosine indicates weak coupling and inefficient cross relaxation. Despite the apparent cross-relaxation effects, all attempts to detect the proton enhancement directly were unsuccessful. Spin-lattice relaxation rates were also measured for Boltzmann (129)Xe in myoglobin. The cross-relaxation rates were determined from changes in (129)Xe relaxation rates in the alpha-cyclodextrin and myoglobin solutions. These cross-relaxation rates were then used to model (1)H signal gains for a range of (129)Xe to (1)H spin population ratios. These models suggest that in spite of very large (129)Xe polarizations, the (1)H gains will be less than 10% and often substantially smaller. In particular, dramatic (1)H signal enhancements in lung tissue signals are unlikely.     

Surface metal-insulator transition on a vanadium pentoxide (001) single crystal

In situ band gap mapping of the V2O5(001) crystal surface revealed a reversible metal-to-insulator transition at 350-400 K, which occurs inhomogeneously across the surface and expands preferentially in the direction of the vanadyl (V=O) double rows. Supported by density functional theory and Monte Carlo simulations, the results are rationalized on the basis of the anisotropic growth of vanadyl-oxygen vacancies and a concomitant oxygen loss driven metal-to-insulator transition at the surface. At elevated temperatures irreversible surface reduction proceeds sequentially as V2O5(001) --> V6O13(001) --> V2O3(0001).     

Property measurement of the CsI(Tl) crystal prepared at IMP

Large-sized CsI(Tl) single crystals, ～φ100mm×350mm, have been grown successfully, and this CsI(Tl) coupled with PD has been successfully utilized at RIBLL (the Radioactive Ion Beam Line in Lanzhou) to measure the energy of heavy ions as a stopping detector. The performances of CsI(Tl) detector coupled with PD and APD have been tested and compared, including the temperature dependence of scintillating light yield.     

Property measurement of the CsI (Tl) crystal prepared at IMP

Large-sized CsI(T1) single crystals,～Φ100 mmx350 mm,have been grown successfully,and this CsI(Tl) coupled with PD has been successfully utilized at RIBLL (the Radioactive Ion Beam Line in Lanzhou)to measure the energy of heavy ions as a stopping detector.The performances of CsI(Tl) detector coupled with PD and APD have been tested and compared,including the temperature dependence of scintillating light yield.     

Shear melting of a hexagonal columnar crystal by proliferation of dislocations

A hexagonal columnar crystal undergoes a shear-melting transition above a critical shear rate or stress. We combine the analysis of the shear-thinning regime below the melting with that of synchrotron x-ray scattering data under shear and propose the melting to be due to a proliferation of dislocations, whose density is determined by both techniques to vary as a power law of the shear rate with a 2/3 exponent, as expected for a creep model of crystalline solids. Moreover, our data suggest the existence under shear of a line hexatic phase, between the columnar crystal and the liquid phase.     

Optical-induced Freedericksz transition of nematic liquid crystal doped with porphyrin (ZnTPP)

In this Letter, we studied the optical-induced Freedericksz transition of 5CB doped with 1% volume fraction of bio-molecule, porphyrinozinc(II) (ZnTPP). Excited by Ti:sappire laser with the 82 MHz repetition rate and 100 fs pulse duration, the optical Freedericksz threshold of a 23.6 μm-thickness planar alignment sample occurred at an intensity level of 0.35 mW/mm² in contrast to the normally observed 83 mW/mm² value for pure 5CB.     

Direct measurement of Au(110) surface structural parameters by low energy ion backscattering

The reconstructed Au(110) surface is studied by ion backscattering at a large scattering angle using a time-of-flight technique. The results agree with the missing row model of the Au(110) surface with a contraction of the first layer with respect to the bulk terminated atomic positions.     

Removal of lead from aqueous solutions by using the natural and Fe(III)-modified zeolite

In the present study, the sorption of lead by the natural and Fe(III)-modified zeolite (clinoptilolite) is described. The characterization of the natural zeolite-rich rock and the Fe(III)-modified form was performed by chemical analysis, point of the zero charge (pH_pzc), X-ray powder diffraction, applying the Rietveld/RIR method for the quantitative phase analysis, and scanning electron microscopy. The effects of sorbents dose and the initial lead concentrations on its sorption by two sorbents were investigated. For both sorbents, it was determined that at lower initial concentrations of lead, ion exchange of inorganic cations in zeolites with lead, together with uptake of hydrogen dominated, while at higher initial lead concentrations beside these processes, chemisorption of lead occurred. Significantly higher sorption of lead was achieved with Fe(III)-modified zeolite. From sorption isotherms, maximum sorbed amounts of lead, under the applied experimental conditions, were 66 mg/g for the natural and 133 mg/g for Fe(III)-modified zeolite. The best fit of experimental data was achieved with the Freundlich model (R² ≥ 0.94).     

Association of octamethyltetra(p-sulfophenyl)porphin and tetra(4-N-methylpyridyl)porphin in aqueous solutions

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 3, pp. 439–444, September, 1991.