In situ ultraviolet Raman spectroscopy of the reduction of chromia on alumina catalysts

A fluidized bed in situ cell is used to examine the chromia on alumina catalyst surface. The loading is varied from 1 to 20% chromium oxide on alumina. The structure of the surface is monitored as a function of temperature, reduction, and hydration. This is the first study to use ultraviolet excitation to study a reduced chromium catalyst surface. Reduction of the sample in hydrogen gas leads to the formation of noncrystalline Cr(3+) species. Addition of potassium to the surface reduces the size of the chromia clusters.     

Nematic phase transitions in mixtures of thin and thick colloidal rods

We report experimental measurements of the phase behavior of mixtures of thin (charged semiflexible fd virus) and thick (fd-PEG, fd virus covalently coated with polyethylene glycol) rods with diameter ratio varying from 3.7 to 1.1. The phase diagrams of the rod mixtures reveal isotropic-nematic, isotropic-nematic-nematic, and nematic-nematic coexisting phases with increasing concentration. In stark contrast to predictions from earlier theoretical work, we observe a nematic-nematic coexistence region bound by a lower critical point. Moreover, we show that a rescaled Onsager-type theory for binary hard-rod mixtures qualitatively describes the observed phase behavior.     

Quantum opacity, the RHIC Hanbury Brown-Twiss puzzle, and the chiral phase transition

We present a relativistic quantum-mechanical treatment of opacity and refractive effects that allows reproduction of observables measured in two-pion Hanbury Brown-Twiss (HBT) interferometry and pion spectra at RHIC. The inferred emission duration is substantial. The results are consistent with the emission of pions from a system that has a restored chiral symmetry.     

Scanning probe lithography on fluid lipid membranes

Scanning probe lithography (SPL) is applied to pattern fluid lipid membranes on a solid borosilicate substrate. Grids of metal lines, prepatterned onto the substrate by electron beam lithography, serve to partition the supported membrane into an array of isolated fluid pixels. By toggling the pH of the surrounding solution, the effect of the probe tip on the membrane can be regulated. Alkaline conditions favor membrane removal, while neutral pH favors membrane deposition. Arbitrary membrane patterns with spatial dimensions limited by the underlying grid size can be constructed by sequential SPL membrane removal followed by refill with a different membrane type. In the present study, bilayers of unique composition fill 1 x 1 mum corrals and were positioned 100 nm apart.     

The location of adsorbed hydrogen in graphite nanostructures

Recent experiments suggest that the high hydrogen storage capacity in graphite nanostructures might be associated with adsorption on the edges. First-principles calculations are used to study the structure and energetics of H chemisorption on graphite zigzag edges. The properties of both singly and doubly hydrogenated edges are examined. Molecular hydrogen can dissociatively adsorb on the edge directly, with small activation barriers to the formation of either singly or doubly hydrogenated structures. A new model for the location of adsorbed H is proposed.     

Speciation studies of nickel and chromium in wastewater from an electroplating plant

A speciation scheme involving the use of flame atomic absorption spectrometry (FAAS) and differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV) techniques was applied to studies of nickel and chromium in wastewater from a nickel-chrome electroplating plant. Dimethylglyoxime (DMG) and diethylenetriaminepentaacetic acid (DTPA) were employed as complexing agents for adsorptive voltammetric determination of Ni and Cr, respectively. Cr(III) and Cr(VI) were determined by exploiting differences in their reactivity towards DTPA at HMDE. Total dissolved metal content was in the range 2906-3141 and 30.7-31.2 mg l⁻¹ for Ni and Cr, respectively. A higher percentage of the metal was present as labile species (mean value of 67.9% for Ni and 79.8% for Cr) suggesting that strongly binding ligands are not ubiquitous in the sample. About 77.8% of Cr was found to exist in the higher oxidization state, Cr(IV). Results on effect of dilution on lability of the metal forms in the sample using DPAdCSV showed slight peak shifts to a more negative (cathodic) value by −0.036 V for Ni and −0.180 V for Cr with a dilution factor of 100, while peak intensity (cathodic current) remained fairly constant.     

Photodissociation of CCH: classical trajectory calculations involving seven electronic states

The photodissociation dynamics of ethynyl radical, C(2)H, involving seven electronic states is studied by classical trajectory calculations. Initial values of the trajectories are selected based on relative absorption intensities calculated by Mebel et al. The energies and the derivatives are interpolated by three-dimensional cubic spline interpolator using an extended data pool. Mean square errors and standard deviations in interpolation of energies for 450 data points are found to be in the range 3.1 x 10(-6)-1.4 x 10(-5) and 1.7 x 10(-3)-3.8 x 10(-3) hartrees, respectively. The photofragments of C(2) and H are produced mainly in the X (1)Sigma(g) (+), a (3)Pi(u), b (3)Sigma(g) (-), c (3)Sigma(u) (+), A (1)Pi(u), B (1)Delta(g) electronic states of C(2) as product. The avoided crossings do not appear to be in the main dissociation pathways. The internal distributions are in good accord with the experimental results where comparison is possible, suggesting that the fragmentation mechanism of C(2)H(2) into C(2) and H is a two step process involving C(2)H radical as an intermediate with a life time long enough to allow complete collection of the phase space in the experiments.     

Fiber-optic-based absolute displacement sensors at 1500 nm by means of a variant of channeled spectrum signal recovery

An absolute displacement-sensing system based on channeled spectrum processing capable of simultaneous interrogation of fiber Bragg gratings and fiber-optic interferometric sensors is presented in which the role of the optical spectrometer is performed by a scanning Fabry-Perot filter. We demonstrate a resolution of +/-50 nm with an estimated dynamic range of 1 part in 10(5).     

Lanthanide transport in stabilized zirconias: interrelation between ionic radius and diffusion coefficient

The diffusion of all stable lanthanides was measured both in calcia stabilized zirconia (CSZ) and in yttria stabilized zirconia (YSZ) in the temperature range between 1,286 and 1,600 degrees C. The lanthanide diffusion coefficients obtained increase with increasing ionic radius. The experimental activation enthalpy of diffusion is near 6 eV for CSZ and between 4 and 5 eV for YSZ and is not strongly affected by the type of lanthanide. The results were correlated with defect energy calculations of the lanthanide diffusion enthalpy using the Mott-Littleton approach. An association enthalpy of cation vacancies with oxygen vacancies of about 1 eV (96 kJ/mol) was deduced in the case of CSZ, while there is no association in the case of YSZ. Furthermore, the change in diffusion coefficients can be correlated to the interaction parameter for the interaction between the lanthanide oxide with zirconia: The higher the interaction parameter, the higher the lanthanide diffusion coefficient.     

Novel search for heavy nu mixing from the beta+ decay of 38mK confined in an atom trap

A new technique, full neutrino momentum reconstruction, is used to set limits on the admixture of heavy neutrinos into the electron neutrino. We measure coincidences between nuclear recoils and positrons from the beta decay of trapped radioactive atoms and deduce the neutrino momentum. A search for peaks in the reconstructed recoil time-of-flight spectrum as a function of positron energy is performed. The admixture upper limits range from 4 x 10(-3) to 2 x 10(-2) and are the best direct limits for neutrinos (as opposed to antineutrinos) for the mass region of 0.7 to 3.5 MeV.