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We have measured the energy and angle differential ejected electron spectra of C60 as well as Ne atoms in collisions with 4 MeV/u bare fluorine projectile ions. Absolute cross sections have been estimated for electron emission in the energy range of 1 eV–300 eV, including the KLL-Auger electrons for various angles between 30° and 150°. The double differential cross sections for C60 have been compared with the state-of-the-art CDW-EIS model under CNDO approximation as well as with the data for the Ne target. The C60 spectra at all angles show a broad giant plasmon resonance in the low energy region, which is not present in the atomic target data. The angular distribution reveals the dipolar nature of the plasmon excitation. The C K-LL Auger emission from C60 reveals a large angular anisotropy compared to that for a hydrocarbon, e.g. methane target.

Projectile angular distributions for electron capture in p + H2 collisions at 25 and 75 keV impact energies, measured by Sharma et al. [Phys. Rev. A 86, 022706 (2012)], are calculated using the CDW-EIS and eikonal approximations. Angular distributions evaluated in the CDW-EIS approximation are in good agreement with the experimental data measured for coherent projectile beams. Incoherent projectile scatterings are also considered by folding the coherent angular distributions over the transverse momentum distribution of the projectile wave-packet. Reasonable agreements with the measurements are obtained only with coherence parameters very different from those reported in the experiments.

International audience; The dynamics of the electron capture by He+ ions from H2 molecule has been investigated in the four-body first Born approximation. Cross sections differential in the scattering angle of the projectile ion have been calculated for various molecular orientations. The calculations account for the interference effects due to the coherent scattering of the particles from the two atomic centers. Total cross sections (integrated over the projectile’s scattering angle and averaged over all the molecular orientations) have also been calculated by a three-body version of the classical trajectory Monte Carlo (CTMC) method based on use of a two-center molecular potential, as well as in a semi-classical quasi-molecular model. The obtained total cross sections are compared with the available experimental data and other theoretical calculations. For impact energies above 40 keV a reasonable agreement has been found between the present theoretical results and the experiment.

The main aim of the project reported in this paper was twofold. One of the primary goals was to produce an extensive source of network data for bibliometric analyses of field dynamics in the case of Computer and Information Science. To this end, we rendered the raw material of the DBLP computer and infoscience bibliography into a comprehensive collection of dynamic network data, promptly available for further statistical analysis. The other goal was to demonstrate the value of our data source via its use in mapping Computer and Information Science (CIS). An analysis of the evolution of CIS was performed in terms of collaboration (co-authorship) network dynamics. Dynamic network analysis covered three quarters of the XX. century (76 years, from 1936 to date). Network evolution was described both at the macro- and the mezo level (in terms of community characteristics). Results show that the development of CIS followed what appears to be a universal pattern of growing into a “mature” discipline.

We develop and analyze an agent-based model for the study of information propagation in dynamic contact networks. We represent information as a state of a node in a network that can be probabilistically transferred to an adjacent node within a single time step. The model is based on a closed (yet sufficiently large) population that can support processes of link generation and annihilation using different contact regimes. Our study is confined to the case of homogeneous contacts, where each agent establishes and breaks contacts in the same way. We consider information to be available for spreading in a fixed time window (i.e. finite memory). We find, surprisingly, that information transmission (measured as the proportion of informed nodes after a fixed number of time steps) is identical for dynamic preferential and random networks, but radically different for the associate mixing contact regime. We also find that the probability of transmission is, similarly counterintuitively, not a main driver of the process as opposed the the main network par maters determining contact lifetime and the turnover rate on connections. We discuss the explanation and the significance of these results in the light of the fundamental difference between dynamic and static (cumulative) networks.

Inspecting the dynamics of networks opens a new dimension in understanding the interactions among the components of complex systems. Our goal is to understand the baseline properties expected from elementary random changes over time, in order to be able to assess the various effects found in longitudinal data. We created elementary dynamic models from classic random and preferential networks. Focusing on edge dynamics, we defined several processes for changing networks of a fixed size. We applied simple rules, including random, preferential and assortative modifications of existing edges – or a combination of these. Starting from initial Erdos-Renyi networks, we examined various basic network properties (e.g., density, clustering, average path length, number of components, degree distribution, etc.) of both snapshot and cumulative networks (for various lengths of aggregation time windows). Our results provide a baseline for changes to be expected in dynamic networks. We found universalities in the dynamic behavior of most network statistics. Furthermore, our findings suggest that certain network properties have a strong, non-trivial dependence on the length of the sampling window.

Suppose you have the possibility to choose to adopt one of a number of different behaviors or to choose to buy one of a number of different products, and suppose your choice is influenced by your individual perception of the average choices made by others. Economists Brock and Durlauf (in Am. Econ. Rev. 92(2):298, 2002; The Economy as an Evolving Complex System III. Oxford University Press, New York, 2006) have derived seminal theoretical results for the equilibrium behavior of the multinomial discrete choice model with social interactions, assuming homogeneous decision-makers, global interactions and laws of large of numbers. The research presented in this paper extends Brock and Durlauf's model to allow for unobserved preference heterogeneity between choice alternatives by studying the nested logit model. Next, by drawing on the computational possibilities permitted through social simulation of multi-agent systems (MAS), this paper relaxes the assumption of global interactions and considers instead local interactions within several hypothesized social and spatial network structures. Additional heterogeneity is thus hereby induced by the influence on a given decision-maker's choice by the particular network connections he or she has and the particular perceived percentages, for example, of the agent's neighbors or socio-economic peers making each choice. Discrete choice estimation results controlling these heterogeneous individual preferences are embedded in a multi-agent based simulation model in order to observe the evolution of choice behavior over time with socio-dynamic feedback due to the network effects. The MAS approach also gives us an additional advantage in the possibility to test size effects, and thus relax the assumption of large numbers, as well as test the effect of different initial conditions. Finally an extra benefit is gained via the MAS approach in that we are not confined to study only the equilibrium behavior, and have the possibility here to observe the time-varying trajectories of the choice behavior. This is important since smaller network sizes are revealed to be associated with higher volatility of the choice behavior in this model, and consequently stochastic cycling between equilibria. Averaged over time, the emergent behavior in such case yields a quite different picture than the theoretical results predicted by Brock and Durlauf. Furthermore being able to observe the emergent behavior allows us to see the subtle role of the unobserved heterogeneity in the nested logit model in breaking the symmetry of the multinomial logit model. We can see the temporal patterns by which theoretically predicted dominant equilibria emerge or not according to different social and spatial network scenarios. With an eye towards application in the context of transportation mode choice, we conclude highlighting limitations of our present study and recommendations for future work.

The continuum distorted-wave model with an eikonal initial state for ionisation is discussed within the framework of the impact-parameter method. Particular attention is paid to the surface term, which describes the transition by a distorting potential, and which has been omitted in all of the previous calculations performed using the model. However, this term is included in the transition amplitude in a recent application of the model based upon a quantum-mechanical treatment. The present study, in which the surface term is evaluated within the impact-parameter method, shows that this term does not contribute to the transition amplitude. In describing the electron-ejection mechanism for a p±–H collision, the cross-sections evaluated using the impact-parameter model show numerical agreement with those determined in the quantum-mechanical version. This agreement indicates that the contribution of the surface term calculated in the wave treatment is negligible over the region in which the impact-parameter model is valid.

Triple differential cross sections (TDCSs) are calculated for the ionization of the hydrogen molecule by electron impact with asymmetric and symmetric kinematical configuration, respectively in coplanar arrangement and in the plane perpendicular to the incident direction. In the scattering plane we explore the angular distribution of the TDCS as well as the dependence of the cross section on the internuclear separation. In the perpendicular plane the TDCSs are investigated as a function of the angular separation between the outgoing electrons and for an equal energy sharing between them.

In addition to the Thomas peak, occurs at 0.47 mrad, another peak has been observed at ≈ 0.75 mrad in a recent measurement for projectile angular differential cross sections of single electron capture in proton-helium collision at impact energies of MeV region [M. Gudmundsson et al., J. Phys. B 43, 185209 (2010)]. Stimulated by this report, the differential cross section is calculated based on the first Born approximation for single ionization of helium by proton impact. Calculations with and without inter-electron correlation give almost the same results, and the peak observed experimentally near 0.75 mrad is not accounted for in the treatment.

The first-order Born approximation with correct boundary condition is applied in a study of the resonant double electron capture by fast He2+ from helium. A configuration-interaction wave function is employed to describe the ground state of helium. Total cross section as a function of the impact energy is calculated and compared with experimental and theoretical values.

Some recent results on the cusp in the electron spectrum and pertaining consequences are discussed. It is shown that the shape of the cusp is determined mainly by the charge of the outgoing projectile at a given impact velocity. The effect of a new approximation for the spectrometer transmission function on the cusp-shape parametersβ1,β2 are also discussed.

The energy dependence of the parameters in the series expansion of the cusp-shape was studied by using the experimental data of the present authors and all the other published data. The recent theoretical interpretations are also discussed.

The theoretical and experimental double differential cross sections for ejected electrons are compared for the 0.5 MeV/u He2+−He, Ne collision systems at backward observation angles. The theoretical values are calculated within the framework of first Born approximation. The agreement between the theoretical and experimental values is rather good for the He, but not for the Ne target.