Electron-hole pair excitation in atom-surface scattering

The inelastic scattering of a light atom (helium) from a metallic surface with creation or annihilation of electron-hole pairs is studied. Diagonal and off-diagonal matrix elements of the atom-metal interaction are discussed. The nonadiabatic contributions to the scattering are analyzed in terms of a statistical potential. Explicit calculations are performed for a jellium model at electron densities corresponding to Al and Na. The electron-hole pair excitation probabilities turn out to be of the order of 10^?5–10^?3.     

‘Counterfactual’ interpretation of the quantum measurement process

The question of the determination of the state of the system during a measurement experiment is discussed within quantum theory, as a part of the more general measurement’s problem. I propose a counterfactual interpretation of the measurement process which answers the question from a conceptual point of view. This interpretation turns out to be consistent with the predictions of quantum theory, but it presents difficulties from an operational point of view.     

Direct determination of adsorption heats

Energy changes occurring during adsorption in gas-solid and solution-solid systems are considered in connection with measurement of the adsorption enthalpies. Some experimental apparatuses allowing determination both of heat evolved and adsorbed amounts are described, with special regard to those using heat-flow microcalorimeters. Calibration techniques and experimental data reliability are also discussed.     

Postcritical Behavior of Cables Undergoing Two Simultaneous Galloping Modes

Abstract. A nonlinear two degree-of-freedom model, describing a flexible elastic suspended cable undergoing galloping oscillations, is analyzed. By using a perturbative approach, the critical conditions occuring for different values of the aerodynamic coefficients are described. Two different type of critical conditions, corresponding to simple or double Hopf bifurcations are found. The nonlinear postcritical behavior of single taut strings in 1:1 primary internal resonance is studied through the multiple scale perturbation method. In the double Hopf bifurcation case the influence of the detuning between the critical eigenvalues on the postcritical behavior is illustrated. It is found that quasi-periodic motions, which are likely to occur in the linear field when the two critical frequencies are incommensurable, are really unstable in the nonlinear range. Therefore, the postcritical behavior of the string consists of stable periodic motions for any detuning values.Sommario. Viene analizzato un modello non lineare a due gradi di libertrappresentativo di un cavo elastico flessibile sospeso alle estremite soggetto ad oscillazioni galoppanti. Utilizzando un approccio perturbativo, vengono descritte le condizioni critiche per differenti valori dei coefficienti aerodinamici. Sono presenti due diversi tipi di condizioni critiche, corrispondenti a biforcazioni di Hopf semplici e doppie. Attraverso il metodo perturbativo delle scale multiple viene studiato il comportamento post-critico non lineare di singole stringhe tese in risonanza interna primaria 1:1. Nel caso di biforcazione doppia di Hopf viene illustrata l'influenza del detuning tra gli autovalori critici sul comportamento post-critico. Si trova che i moti quasi-periodici, presenti in campo lineare quando le due frequenze critiche sono incommensurabili, sono in realtinstabili in campo non lineare. Quindi, il comportamento post-critico della stringa risulta composto da moti periodici stabili per un qualsiasi valore del detuning.     

Good reduction of elliptic curves defined over\mathbb{Q}(\sqrt[3]{2})

Partially supported by Ministero della Pubblica istruzione—Italia. Consiglio Nazionale delle Ricerche—Italia.     

Deformation field induced by spherical indentation: numerical analysis and experimental measurement by speckle interferometry

The present paper describes an experimental procedure for the measurement of the displacement field around a spherical indentation. The measurements were performed by a speckle interferometer designed for the detection on small areas of one or more oblique components of displacement; the indentations were made by a standard durometer used for metals.The experiments were carried out on a hardened and tempered steel, previously characterized by a standard tensile test; the results are in accordance with the numerical results obtained by an elasto-plastic FEM analysis.     

Paradigms and falsification in earthquake engineering

Particular reference is made to the works by E. Torroja and by A. M. Freudenthal, that can be seen as the father-works of a new paradigm in the study of structural engineering: the probabilistic approach to structural safety. The key idea of this approach is, according to Freudenthal, the selection of an acceptable risk of failure. The criteria that have been proposed for this selection in the case of constructions in earthquake-prone areas are discussed.Attention is then paid to the scientific reliability of seismic hazard analysis at a particular site, following the teachings of modern philosophy of science. The problem is discussed in the frame of the theory of falsification, due to K. Popper and I. Lakatos: it is recognised that the results of a seismic hazard analysis are not falsifiable; hence, they would not have a scientific status. In order to overcome this problem, it is proposed to shift the attention from the final results of the hazard analysis, which are not directly falsifiable, to the procedures which lead to that result. A method for falsifying these procedures is proposed.Invited lecture presented (in Italian) at the 4th Specialist Meeting of the Stochastic Mechanics Group of AIMETA, Rome, April 1990.