Age-usage semi-Markov models

This paper presents a non-homogeneous age-usage semi-Markov model with a measurable state space. Several probability functions useful to assess the system’s reliability are investigated. They satisfy the same family of equations we call indexed Markov renewal equations. Sufficient conditions to assure the existence and uniqueness of their solutions are provided. The numerical analysis of these equations is executed through the construction of a process discrete in time and space, which is shown to converge to the continuous one in the Skorohod topology. An algorithm useful for solving the discretized system of equations is presented by using a matrix representation.     

Symmetries of BLT-Sets

We do the tentative beginnings of a study of BLT-sets of generalised quadrangles via their symmetries. In particular, the study of whorls about a line leads us to hyperbolic reflections preserving a BLT-set of Q(4, q).     

Maximal Partial Spreads and Flocks

Denote by a flock of a quadratic cone of PG(3,q) by S() the spread of PG(3,q) associated with and by l the common line of the base reguli. Suppose that there are two lines not transversal to a base regulus which share the same lines of S() Then we prove that is either linear or a Kantor-Knuth semifield flock. Using this property we can extend the result of J3 on derivable flocks proving that, if a set of q + 1 lines of S() defines a derivable net different from a base regulus-net, then is either linear or a Kantor-Knuth semifield flock. Moreover if l is not a component of the derivable net, then is linear.     

Co stretching vibration of carbon monoxide adsorbed on nickel(111) studied by high resolution electron loss spectroscopy

The frequency of the v-CO stretching vibration measured by HRELS has been followed as a function of the CO coverage and in the presence of coadsorbed hydrocarbons on the Ni(111) face. The v-CO frequency shifts continuously from 225 meV (1814 cm^?1) to 237 meV (1911 cm^?1) when the CO coverage increases from 0 to 0.41. Coadsorption of electron donor molecules, such as ethylene and benzene, generates a significant lowering of the v-CO frequency. Results are discussed in terms of the back donation of metallic electrons into the 2π ¹ antibonding orbitals of CO, the dipole-dipole coupling and the coordination number of the CO adsorbed molecules. The back donation is found to play the major role in the range of coverage explored but we cannot exclude some contribution of a dipole-dipole coupling effect.     

Bulk and surface core level binding energies in the Pt80Fe20(111) alloy

Core level photoemission spectroscopy of the Pt 4f_7/2 level is used to investigate the surface and bulk Pt environments in the ordered catalytic alloy Pt₈₀Fe₂₀. The results obtained support a LEED model of Pt segregation to the surface. This implies the presence of two Pt surface sites.     

Pd8Ni92(1 1 0) surface structure from surface X-ray diffraction. Surface evolution under hydrogen and butadiene reactants at elevated pressure

The (N × 1) reconstruction (N = 5-6) of the clean Pd₈Ni₉₂(1 1 0) surface has been investigated by surface X-ray diffraction. A good fit with experimental data collected under UHV conditions is obtained when introducing undulations in the outer dense rows, constituted mainly of Pd atoms which strongly segregate to the surface. This reconstruction can be regarded as a way to relax the strains induced on the bigger Pd surface atoms, at least partially. The modifications of the surface were studied under butadiene then hydrogen as well as during butadiene hydrogenation at elevated pressure at 300 K and the (N × 1) reconstruction was found to be still present. The main changes are observed under pure hydrogen and during butadiene hydrogenation.