Isotopic exchange of CO adsorbed on Pt(111)

The isotopic exchange of CO adsorbed on Pt(111) was studied using polarization modulation IR reflection absorption spectroscopy (PM-IRRAS) and temperature programmed desorption. It was found that the rate constants for the exchange reaction are much higher than would be expected from previous investigations of CO adsorbed on Pt nanoparticles. The adsorption of CO on Pt(111) under elevated pressures of CO and H(2) was also studied using PM-IRRAS. It was seen that CO pressures above 1 mbar lead to a shift in the absorption peak arising from CO adsorbed on a bridge site from 1850 to 1875 cm(-1). Exposing the CO-covered Pt(111) surface to 1000 mbar H(2) did not lead to any significant desorption of CO at room temperature, whereas at 363 K H(2) exposure did lead to a significant desorption of CO, due to the increased chemical potential of H(2). In a mixture of CO and H(2) with partial pressures of 0.01 mbar and 1000 mbar, respectively, no significant effect of H(2) on the PM-IRRAS spectrum was seen at temperatures below 423 K.     

Algorithms for cardinal interpolation using box splines and radial basis functions

Summary We describe an algorithm for (bivariate) cardinal interpolation which can be applied to translates of basis functions which include box splines or radial basis functions. The algorithm is based on a representation of the Fourier transform of the fundamental interpolant, hence Fast Fourier Transform methods are available. In numerical tests the 4-directional box spline (transformed to the characteristical submodule of ²), the thin plate spline, and the multiquadric case give comparably equal and good results.     

Condensation of a one-dimensional lattice gas

We consider a one-dimensional lattice gas in the canonical ensemble with interaction energy 1/r , 1<2. Using an energy-entropy argument we show that the gas condenses at sufficiently low temperatures meaning that the gas has a non-uniform density in the thermodynamic limit.Research supported by the Swedish research councils NFR and STUF     

Monte Carlo simulation of phase separation and clustering in the ABV model

As a model for a binary alloy undergoing an unmixing phase transition, we consider a square lattice where each site can be either taken by an A atom, a B atom, or a vacancy (V), and there exists a repulsive interaction between AB nearest neighbor pairs. Starting from a random initial configuration, unmixing proceeds via random jumps of A atoms or B atoms to nearest neighbor vacant sites. In the absence of any interaction, these jumps occur at jump rates _A and _B, respectively. For a small concentration of vacancies (c _v=0.04) the dynamics of the structure factorS(k,t) and its first two momentsk ₁(t),k ₂ ² (t) is studied during the early stages of phase separation, for several choices of concentrationc _B of B atoms. Forc _B=0.18 also the time evolution of the cluster size distribution is studied. Apart from very early times, the mean cluster sizel(t) as well as the moments of the structure function depend on timet and the ratio of the jump rates (= _B/ _A) only via a scaled timet/(). Qualitatively, the behavior is very similar to the direct exchange model containing no vacancies. Consequences for phase separation of real alloys are briefly discussed.     

Prompt fission induced by antiproton annihilation at rest on heavy nuclei

Antiproton induced fission probabilities of U²³⁸, Bi²⁰⁹, Pb²⁰⁸ and Au¹⁷⁷ are reported together with the mass distribution of the fission fragments in the U²³⁸ and Bi²⁰⁹ cases. The charged particles multiplicities observed in co-incidence with fission have, also, been measured for U and Bi and are presented.Dedicated to Peter Armbruster on the occasion of his 60th birthday in recognition of his important contribution to modern Nuclear Physics     

Bianchi type V perfect fluid cosmologies

Bianchi type V solutions of the Einstein equations are studied using the Hamiltonian approach. Explicit expressions depending on a single quadrature are given for the metric components in the general orthogonal perfect fluid case. It is shown that the quadrature can be evaluated in terms of elementary or elliptic integrals when the parameter in the equation of statep=(–1) takes the values 1, 10/9, 4/3, 14/9, 5/3, 2.     

A new perspective on beta-sheet structures using vibrational Raman optical activity: from poly(L-lysine) to the prion protein

The vibrational Raman optical activity (ROA) spectrum of a polypeptide in a model beta-sheet conformation, that of poly(l-lysine), was measured for the first time, and the alpha-helix --> beta-sheet transition monitored as a function of temperature in H(2)O and D(2)O. Although no significant population of a disordered backbone state was detected at intermediate temperatures, some side chain bands not present in either the alpha-helix or beta-sheet state were observed. The observation of ROA bands in the extended amide III region assigned to beta-turns suggests that, under our experimental conditions, beta-sheet poly(L-lysine) contains up-and-down antiparallel beta-sheets based on the hairpin motif. The ROA spectrum of beta-sheet poly(L-lysine) was compared with ROA data on a number of native proteins containing different types of beta-sheet. Amide I and amide II ROA band patterns observed in beta-sheet poly(L-lysine) are different from those observed in typical beta-sheet proteins and may be characteristic of an extended flat multistranded beta-sheet, which is unlike the more irregular and twisted beta-sheet found in most proteins. However, a reduced isoform of the truncated ovine prion protein PrP(94-233) that is rich in beta-sheet shows amide I and amide II ROA bands similar to those of beta-sheet poly(L-lysine), which suggests that the C-terminal domain of the prion protein is able to support unusually flat beta-sheets. A principal component analysis (PCA) that identifies protein structural types from ROA band patterns provides a useful representation of the structural relationships among the polypeptide and protein states considered in the study.     

Gas chromatographic analysis of flunixin in equine urine after extractive methylation

A quantitative method for the analysis of flunixin, 2-(2-methyl-3-trifluoromethylanilino) nicotinic acid, in equine urine by gas chromatography with nitrogen-phosphorus detection has been developed. Flunixin and the internal standard, mefenamic acid, N-(2,3-xylyl) anthranilic acid, were analysed after extractive methylation of the carboxylic acid group using methyl iodide. The extraction and alkylation conditions of flunixin and mefenamic acid have been studied. The detection limit of the method was 0.25 mumol/l flunixin in urine (74 ng/ml). Flunixin was found to be conjugated to 96.5% in equine urine, and the conjugate was spontaneously hydrolysed to free flunixin. This approach can also be used to confirm the presence of flunixin or mefenamic acid in horse urine in the doping control of racehorses.