Small-angle neutron scattering data on C60 clusters in weakly polar solutions of fullerenes

Solutions of fullerence C₆₀ in carbon disulfide CS₂ have been investigated by small-angle neutron scattering. Combination of solubility, contrast, and incoherent scattering make it possible to measure and analyze the relatively small scattering cross section of this system. Along with single fullerene molecules, a small amount of large fullerene clusters (more than 100 Å in size) is found in these solutions. The formation of these clusters depends on the procedure of solution preparation. The size distribution functions of clusters are compared with the results of the phenomenological cluster model of fullerene solubility.     

A monopole mass filter with a hyperbolic V-shaped electrode

In this article we compare the classical monopole mass filter of von Zahn and the monopole mass filter with a hyperbolic V-shaped electrode. The experimental results and those of computer simulation for both mass spectrometers are presented. We show that the replacement of a conventional 90 degrees V-shaped electrode by an electrode with a hyperbolic profile substantially improves the peak shape of any given mass, and increases the mass resolution by a factor of 3-4 and the abundance sensitivity by a factor of 100. The potential of high analytical performance combined with electroforming techniques for electrode manufacture indicate future practical uses of such instruments. Copyright 1999 John Wiley & Sons, Ltd.     

Possible levels of reducing radio wave reflection from an aerodynamic object covered by an absorbing plasma

We estimate the possible levels of reducing backward reflection of radio waves from an aerodynamic object covered by an absorbing plasma created on the object at tropospheric flight altitudes. This effect is analyzed in terms of a model one-dimensional problem of radio wave propagation in inhomogeneous layers of absorbing plasma. 5th Central Testing Institute of the Department of Defense of the Russian Federation, Voronezh, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 9, pp. 893–899, September, 1999.     

Polypropylene,modified with some oligoesters

Miscibility of polypropylene with some oligoesters was evaluated by optical wedge interference microscopy. Mechanical, thermal, rheological and relaxation properties were studied. Compatibility between the polymers and modifying agents was shown to have a marked effect on stress-strain properties as well as on the structure and melting characteristics of the modified polymers.     

Synthesis and Structural Determination of the Disordered Bixbyite Cu3‐xSb1+xO5.5+3x/2 with Spin‐Glass Behaviour

The ternary copper antimony oxide Cu_3‐xSb_1+xO_5.5+3x/2 (x=0.23) has been synthesized under 0.8–1.3 MPa pO₂ at 1022–1082 °C. Rietveld refinements of X‐ray and neutron powder diffraction patterns concluded that the oxide adopts a bixbyite type structure, crystallising in the cubic space group Ia‐3 with the unit cell parameter a=9.61164(4) Å at room temperature from powder neutron diffraction data. The cationic 8b and 24d sites were found to be occupationally disordered where both Cu and Sb could be found on both sites. This is supported by X‐ray absorption spectroscopy experiments showing more than one possible Cu environment. There was a significant net deficiency of oxygen in the compound which was first inferred from observations of a thermochromic‐like phenomena and also seen from in situ high temperature neutron diffraction experiments. Magnetic susceptibility and magnetization measurements show paramagnetic behaviour with spin‐glass like transition below 6 K.     

The specific surface area and porous structure of graphite materials

Transformations of the specific surface area and porous structure of carbon materials based on graphite were studied by low-temperature adsorption of nitrogen. Exfoliated graphite and graphite foil were found to have a developed (compared with the initial graphite) surface (up to 90 m²/g) and a porous structure formed by slit-like mesopores with a characteristic radius of ∼20 ?. The determining influence of the method of synthesis on the adsorption properties of materials was demonstrated for the first time. Original Russian Text ? O.N. Shornikova, E.V. Kogan, N.E. Sorokina, V.V. Avdeev, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 6, pp. 1161–1164.     

Investigation of the tripoli porous structure by small-angle neutron scattering

The characteristics of the tripoli porous structure have been investigated by small-angle neutron scattering (SANS). Tripoli is a finely porous sedimentary rock formed by small spherical opal particles. Its main component is aqueous silica SiO₂ · nH₂O (80–90%). Tripoli is widely used in practice as a working medium for sorption filters and in some other commercial and construction technologies. The shape of the experimental SANS curves indicates the presence of small and large pores in tripoli. The small-pore size was estimated to be ～100 Å. The size of large pores turned out to be beyond the range of neutron wave vector transfers Q that are available for the instrument used; however, their size was indirectly estimated to be ～(2000–2500) Å. The pores of both groups behave as surfacetype fractal scatterers with the fractal dimension D ～ 2.2‐2.6. The densities of pores of these two groups differ by approximately three orders of magnitude (～10¹⁶ and ～10¹³ cm^?3 for small and large pores, respectively); the fraction of large pores amounts to 70–80% of the total pore volume. The found pore characteristics (their densities, sizes, and relative volumes) are in satisfactory agreement (when a comparison is possible) with the absorption data.     

On Enhancement of the Adsorption-Layer Effect at the Metallic Electrode−Liquid Electrolyte Interface in Specular Neutron Reflectometry Experiments

The possibilities for optimizing the substrate/electrode/electrolyte structure are considered in order to obtain the maximum change in the specular-reflection curves obtained in neutron reflectometry experiments at the electrochemical interfaces between a metallic electrode and liquid electrolyte containing Li⁺ ions during their operation. The characteristic relations between the scattering length densities of the components, for which the reflection curves most fully provide information about the structure of the solid electrolyte interphase layer formed on the electrode surface during the charge–discharge processes, are determined and analyzed.     

Influence of the donor concentration on the decay kinetics of sensitized phosphorescence of 1,3,5-triphenylbenzene in toluene at 77 K

Dependence of the kinetics of sensitized phosphorescence (SP) of 1,3,5-triphenylbenzene (1,3,5-TPB) on the concentration of the energy donor – benzophenone (BP) – is studied in toluene at 77 K. An increase in the SP decay rate of 1,3,5-TPB with concentration is established. It is demonstrated that the reason for the increase in the decay rate is the increased radiative deactivation rate constant of triplet excitations caused by exchange interactions. The coefficient characterizing the exponential dependence of the radiative deactivation rate constant for triplet excitations of 1,3,5-TPB on the intermolecular distance in the donor-acceptor pair is determined.     

On the Space of Almost Convergent Sequences

Mathematical Notes -