An experimental study of crystallization and crystal growth of methane hydrates from melting ice

An experiment with well defined gas-water interfacial surface area was developed to study the crystallization and crystal growth of methane hydrates. Measurable formation rates were observed only when melting ice was involved. No hydrates nucleated from liquid water or from non-melting ice. It is concluded that melting ice, which like hydrate water is hydrogen-bonded, provides a template for hydrate nucleation as well as providing a heat sink for absorbing the heat of formation during hydrate growth. The experiment was conducted in the absence of mixing so that hydrate crystals grew under quiescent conditions.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

Determination of the branching ratiosΓ(K L→3π0)/Γ(K L→π+ - 0) andΓ(K L→3π0)/Γ(K L→πev)

Improved branching ratios were measured for theK _L3⁰ decay in a neutral beam at the CERN SPS with the NA31 detector:

Application of novel pressure-sensitive paint formulations for the surface flow mapping of high-speed jets

The principle of pressure-sensitive paints (PSPs) is based upon excitation of the luminophore molecules at a certain wavelength and the emission of this absorbed energy at a higher wavelength. By isolating these two wavelengths we insure that the results obtained are not affected by any background radiation. Various international research groups, such as: the Central Aero-Hydrodynamic Institute (Russia), the University of Washington, NASA Ames, Boeing and McDonnell Douglas (USA), have developed their PSP formulations and some are commercially available.Two paints, which have been developed in-house at the Aero-Physics Laboratory (APL) at the University of Manchester, are studied here. One formulation uses hydrochloric acid (PSP1–HCl) and the other acetone as the solvent (PSP2–Ace). The current study employs the well known schlieren photography technique together with the relatively new PSP method, with comparison to discrete measurements, to examine the flow through a two-dimensional air-ejector system and examines the efficacy of the PSP formulations in providing an accurate global pressure field of the aforementioned setup. Detailed analysis of the errors and drawbacks involved in PSP measurements along with possible solutions to overcome them are also presented. Fully expanded jet Mach numbers in the range of 0.52 ? M_j ? 1.36 were examined.     

Matrix‐assisted laser desorption/ionization time‐of‐flight analysis of the copolymerization reaction of an expanding monomer with a diepoxide

In search of a composite with low stress and low shrinkage properties, this study includes matrix‐assisted laser desorption/ionization time‐of‐flight analysis of the photoinitiated cationic polymerization between an expanding monomer [1,5,7,11‐tetraoxaspiro[5.5]undecane (TOSU)] and a diepoxide [bisphenol A diglycidyl ether (BADGE)]. Past studies using NMR and differential scanning calorimetry analyses concluded copolymerization indirectly on the basis of deviations from homopolymer product data. This is the first study to provide direct evidence of copolymerization between these species. Unlike previous research, this study enables the identification of the TOSU homopolymer and the absence of the BADGE homopolymer, suggesting initial cationic activation of TOSU. In addition to peaks that correspond to the presumed mechanism for six‐membered TOSU polymerization, many peaks have a net gain or loss of cyclic carbonate in support of a new polymerization mechanism participating in the reaction. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5962–5970, 2005     

Sommerschule „Frontiers of Polymer Chemistry”︁

38 indische Studenten sowie 12 Dozenten, davon 5 von deutschen Universitäten oder außeruniversitären Forschungsinstituten, haben Ende Juni/Anfang Juli an der zweiwöchigen, vom DAAD finanzierten Sommerschule „Frontiers of Polymer Chemistry”︁ am Indian Institute of Science (IISc) in Bangalore teilgenommen. Der Anstoß zu dieser Veranstaltung kam von Ullrich Scherf, Makromolekulare Chemie, Universität Wuppertal und S. Ramakrishnan, Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore/Indien.     

Highly charged ion Coulomb crystallization in mixed strongly coupled plasmas

The investigation of highly charged ion Coulomb crystallization in mixed strongly coupled plasmas is of interest in many areas: white dwarf astrophysical plasmas are believed to have very similar thermodynamic properties, cold highly charged ions can be used as an object for high precision laser spectroscopy of fine and hyperfine transitions in the visible due to the absence of Doppler broadening and, an entirely new area of research is the potential application to highly charged ion based quantum computing schemes. We report the formation of such plasmas in a cryogenic Penning trap. These plasmas consisting of many species including Be⁺ and Xe⁴⁴⁺ or Be⁺ and Xe¹⁵⁺ ions, are formed at a temperature of less than 4 K. The temperatures were obtained by applying a laser based sympathetic cooling scheme. The determination of the temperature and density from the laser resonance width and the fluorescence imaging of the Be⁺ clouds, respectively, yields a Coulomb coupling constant for the centrifugally separated Xe plasma high enough for crystallization. A molecular dynamics code, developed just for this purpose, was run to clarify the understanding of these plasmas and it was possible to show consistency between experiment and simulation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reduction of vanadium(V) by L-ascorbic acid at low and neutral pH: kinetic, mechanistic, and spectroscopic characterization

L-Ascorbic acid interacts with vanadium(V) over the pH range of 0.4-7.0 to form three different coordination complexes. Both inner- and outer-sphere electron-transfer pathways are proposed to form vanadium(IV) complexes with L-ascorbate or dehydroascorbate, respectively. Effects of the pH on the coordination of L-ascorbic acid to the vanadium(V) center were observed and are presumably related to the speciation of the vanadium(V) ion. Three vanadium(IV) complexes were observed using ambient-temperature electron paramagnetic resonance spectroscopy. Two of these complexes are proposed to be vanadium(IV) L-ascorbate complexes, and one is consistent with a vanadium(IV) dehydroascorbic acid complex proposed earlier. These reduction reactions will occur under physiological conditions and could be important to the reduction of vanadium(V)-containing coordination complexes used as insulin-enhancing agents for treatment of diabetes.     

Synthesis, Characterization, and Luminescence Spectroscopic Accessibility Studies of tris(2,2′-Bipyridine)Ruthenium(II)-Labeled Inorganic-Organic Hybrid Polymers

The modified tris(2,2-bipyridine)ruthenium(II) complex 2 was anchored via a sol-gel process to different polysiloxane matrices to give a series of novel inorganic–organic hybrid polymers. One of the bipyridine ligands of 2 was provided with a long-chain spacer carrying a triethoxysilyl function (T group) at the end, which enables almost free mobility of the transition metal center. The polymers were swollen in several organic solvents of different polarity to investigate the luminescence behavior in the presence of quencher molecules. The luminescence of 2 was quenched using anthracene and atmospheric oxygen in appropriate concentrations of 5 · 10^–4 to 5 · 10^–3 and 3 · 10^–3 M, respectively. The luminescence behavior of 2 was determined by steady-state and time-resolved luminescence experiments. Translational mobilities of molecular species dissolved in the liquid phase were investigated by the kinetics of luminescence quenching after laser excitation. Both the translational mobility of anthracene and atmospheric oxygen, specified with the rate constant k₂ and the percentage of accessible luminescent centers were determined. Translational mobilities and the accessibility for anthracene and atmospheric oxygen in hybrid materials are significantly higher than in conventional Q type polysiloxanes.