The influence of an electron beam on oxidation of polycrystalline nickel surfaces,monitored by disappearance potential spectroscopy (DAPS)

Disappearance Potential Spectroscopy (DAPS) measurements are performed on clean nickel and on nickel during oxidation. The effect of electron bombardment of the surface during oxudation is investigated. An enhanced oxidation of a factor 5 by electron bombardment is observed. The influence of the surface temperature on the DAP spectra is investigated. A visible shift of the L_III and L_II binding energies is observed near the Curie temperature. This is explained by a change of the energy level configuration of the nickel surface.     

Ion-pair formation in some potassium—molecule collisions. Dependence on the vibrational energy

State-specific cross sections for ion-pair formation in collisions of potassium with halogen and methylhalogen molecules are obtained by means of an inverse Laplace transform. This transform was applied to the total cross sections measured as a function of the temperature of the molecules and the translational energy. The efficiencies of the translational energy and internal energy are compared. The behaviour of the post-threshold region is discussed assuming strong stretching or even dissociation in the ionic channel.     

Effective interactions cannot replace solvent effects in a lattice model of proteins

Protein folding and protein design are among the most challenging problems of the past ten years in biophysics and molecular biology. For a given protein, it is possible to extract, from existing protein databases, a set of specific (i.e., belonging to the investigated protein) effective amino-acid (AA) interactions able to stabilize the native state. On the other hand, attempts to find global effective AA interactions, which would be able to stabilize all proteins at once, failed. Using a simple lattice model where the solvent degrees of freedom are (semi)explicitly taken into account, we show that the absence of global effective AA interactions is due to the solvent and that on this lattice model the solvent effects cannot be reproduced by amino-acid effective interactions.     

Differential cross sections for collisions of negative halogen ions and alkali atoms

In this paper we present the relative differential cross sections for collisions of several negative halogen ions with Na and K. The measurements have been carried out in two separate experiments with energy ranges of 5–150 eV and 500–1000 eV and angular ranges of 0-35° and 0-0.3°, respectively. It is shown that in both of these experiments elastic scattering is the dominant process. No significant inelastic contribution to the differetial cross section, especially no electron detachment, has been observed. The measured differential cross sections are used to obtain information on the anion intermolecular potentials. Comparison of these potentials with the potentials of the neutral molecules shows that all systems investigated have a positive electron affinity over a wide range of internuclear distances. An approximately linear relationship between the dipole moments and the electron affinities is obtained for the halides of the specific alkalis.     

The pumping of an X-ray laser by means of an optical laser

A new mechanism for pumping of an X-ray laser by an optical laser is suggested. The inverse population between the inner levels of atoms is attained by means of the use of fast laser plasma electrons.     

Intercomparison of monochromatic source facilities for the determination of the relative spectral response of erythemal broadband filter radiometers

The relative spectral responses of erythemally weighted broadband radiometers determined at three different laboratories are compared, and the systems are described. The results of measurements of four different broadband radiometers are discussed. Although the common dynamic range of the measured relative spectral responses is approximately 10(4), the differences in the relative spectral response functions are lower than 20%. These differences are related mostly to measurement uncertainties and differences in the spectral response facilities.     

Divergence-free finite elements for the numerical solution of a hydroelastic vibration problem

In this paper, we analyze a divergence-free finite element method to solve a fluid–structure interaction spectral problem in the three-dimensional case. The unknowns of the resulting formulation are the fluid and solid displacements and the fluid pressure on the interface separating both media. The resulting mixed eigenvalue problem is approximated by using appropriate basis of the divergence-free lowest order Raviart–Thomas elements for the fluid, piecewise linear elements for the solid and piecewise constant elements for the interface pressure. It is proved that eigenvalues and eigenfunctions are correctly approximated and some numerical results are reported in order to assess the performance of the method.     

Discrete breathers in nonlinear network models of proteins

We introduce a topology-based nonlinear network model of protein dynamics with the aim of investigating the interplay of spatial disorder and nonlinearity. We show that spontaneous localization of energy occurs generically and is a site-dependent process. Localized modes of nonlinear origin form spontaneously in the stiffest parts of the structure and display site-dependent activation energies. Our results provide a straightforward way for understanding the recently discovered link between protein local stiffness and enzymatic activity. They strongly suggest that nonlinear phenomena may play an important role in enzyme function, allowing for energy storage during the catalytic process.