Raman spectroscopic investigation of H2, HD, and D2 physisorption on ropes of single-walled, carbon nanotubes

We have observed the S- and Q-branch Raman spectra of H2, HD, and D2 adsorbed at 85 K and pressures up to 8 atm on single-walled, carbon nanotubes (SWNT). Comparative data for H2 on graphite and C60 were also collected. Frequency-downshifted and upshifted features were observed in the Q-branch spectra of H2 on C60 and SWNT. These shifts are small and are therefore inconsistent with charge transfer. An H2-surface potential with van der Waals and electrostatic terms was developed and used to estimate the shifts in the frequency of the Q(0) transition of H2 adsorbed in two types of sites. These calculations corroborate the experimental findings and indicate physisorption in multiple sites of the SWNT ropes.     

Signal depression in electrothermal atomic absorption spectrometry by nitrate and sulfate ions

The effects of nitrates and sulfates, which decompose to generate oxidants on heating, on the gaseous atom concentration for Ag,Cu and Ga have been investigated with a graphite filament atomizer and an optical arrangement which allows spatial information above the atomizer surface to be gathered. For the potassium and sodium salts, the largest signal depression, caused by gaseous atom oxidation, was found with the largest relative decomposition at the particular temperature, which therefore gives the largest partial pressure of the oxidants formed above the oxidizer. For the calcium salts, Ca metal was vaporized from the atomizer and competed successfully with the analyte, for any oxidants generated, thereby preventing oxidation of the analyte, so that, in some cases, the analyte atom concentration was increased.     

Global and local fluctuations in multiplicity and transverse energy for central ultra-relativistic heavy-ion interactions

We present results from a comparison between experimental data and model calculations, in this case represented by the Fritiof model, regarding global and local fluctuations in the distributions of transverse energy and charged particle multiplicity. The results indicate that the observed fluctuations originate predominantly from the distribution of emitting sources, i.e. either the number of participating nucleons or the number of binary collisions. The apparently larger widths of the distributions observed in restricted regions of phase space, are explained to be of purely statistical nature. As a result of the analysis the cross section for events with energy densities much larger than the typical value for a central collision is limited. The very small scales, normally associated with studies of intermittent behaviour, are not within the scope of this paper. The results of the analysis are essentially independent of whether intermittence is of importance in the reactions or not.     

Category theoretic properties of fuzzy topological spaces

In this paper we establish some important category theoretic properties, in particular smallness conditions, for categories of fuzzy topological spaces. We also obtain a non-existence of compactifications.     

Recovery of cellulases after hydrolysis by adsorption on steam-pretreated willow

Applied Biochemistry and Biotechnology -     

Raman scattering from potassium iodide near the melting point

We have measured the Raman spectrum of potassium iodide in the crystalline phase at high temperatures, and in the melt. As temperature increases the various second order features in the low temperature spectra coalesce into a broad feature, which persists into the melt. A smooth, quasi-exponential wing also appears in the melt. Thus, the spectrum is structurally similar to those found in solid electrolytes and silver halide melts. Possible interpretations of the spectrum are indicated.     

Transverse energy production in the target fragmentation region in16O-nucleus reactions at 60 and 200A GeV

Charged pion yields and transverse energies of baryons are measured for the reaction¹⁶O+Cu, Ag, Au at 60 and 200A GeV bombarding energy in the target fragmentation region employing the Plastic Ball detector. Only little dependence of the measured quantities on the bombarding energy is found. The data are compared with the multi-chain fragmentation model of Ranft. As a result it turns out that a leading order formation zone cascade is not sufficient to explain the baryon yield and the transverse energies of baryons in the target fragmentation region.     

Raman scattering as a probe of phonon confinement and surface optical modes in semiconducting nanowires

Raman scattering is shown to be an effective probe of optical and surface optical phonons in highly crystalline semiconducting nanowires (SNWs). We show that the confinement model of Richter et al. well describes the nanowire diameter dependence of the asymmetric broadening of the one-phonon band in Si nanowires observed at ∼520 cm^-1. We also show that the use of high laser flux (∼0.1 mW/μm²) leads to a second mechanism that can asymmetrically broaden the 520 cm^-1 Raman band. This broadening has nothing to do with confinement, and can qualitatively be understood in terms of inhomogeneous laser heating. A model is presented that supports this explanation. The production of SNWs via the vapor–liquid–solid growth mechanism leads, in many cases, to an instability in the nanowire diameter or cross-sectional area. In the second part of this review, we show that this instability activates the surface optical (SO) phonon Raman scattering. Examples of this phenomenon are shown for GaP and ZnS nanowires. The former and latter have, respectively, cylindrical and rectangular cross sections. We show that the cross-sectional shape of the nanowire is important for a quantitative analysis of these SO modes. PACS 78.67.-n; 78.67.Lt; 78.30.-j; 78.30.Fs; 72.10.Di