f(R,L m ) gravity

We generalize the f(R) type gravity models by assuming that the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar R and of the matter Lagrangian L _m . We obtain the gravitational field equations in the metric formalism, as well as the equations of motion for test particles, which follow from the covariant divergence of the energy-momentum tensor. The equations of motion for test particles can also be derived from a variational principle in the particular case in which the Lagrangian density of the matter is an arbitrary function of the energy density of the matter only. Generally, the motion is non-geodesic, and it takes place in the presence of an extra force orthogonal to the four-velocity. The Newtonian limit of the equation of motion is also considered, and a procedure for obtaining the energy-momentum tensor of the matter is presented. The gravitational field equations and the equations of motion for a particular model in which the action of the gravitational field has an exponential dependence on the standard general relativistic Hilbert–Einstein Lagrange density are also derived.     

An E.L.S., A.E.S. and L.E.E.D. study of the interaction of O2 with Pd(111) surface

The interaction of oxygen with a Palladium (111) single crystal has been studied using L.E.E.D., A.E.S., E.L.S. techniques at room temperature in the range 10^-7 to 1 torr. Various amounts of two types of chemisorbed oxygen (well-ordered and disordered) are detected. The characteristic energy losses are attributed to different electronic states : surface , volume and particular states induced by oxygen.