An intruder model for verifying termination in security protocols

We formally describe an intruder that is suitable for checking fairness properties of security protocols. The intruder is proved to be equivalent to the Dolev-Yao intruder that respects the resilient communication channels assumption, in the sense that, if a fairness property holds in one of these models, it also holds in the other

A constructive proof of the Heine-Borel covering theorem for formal reals

The continuum is here presented as a formal space by means of a finitary inductive definition. In this setting a constructive proof of the Heine-Borel covering theorem is given

The Audit Logic: Policy Compliance in Distributed Systems

We present a distributed framework where agents can share data along with usage policies. We use an expressive policy language including conditions, obligations and delegation. Our framework also supports the possibility to refine policies. Policies are not enforced a-priori. Instead policy compliance is checked using an a-posteriri auditing approach. Policy compliance is shown by a (logical) proof that the authority can systematically check for validity. Tools for automatically checking and generating proofs are also part of the framework.\u

An Audit Logic for Accountability

We describe and implement a policy language. In our system, agents can distribute data along with usage policies in a decentralized architecture. Our language supports the specification of conditions and obligations, and also the possibility to refine policies. In our framework, the compliance with usage policies is not actively enforced. However, agents are accountable for their actions, and may be audited by an authority requiring justifications.Comment: To appear in Proceedings of IEEE Policy 200

Evidence for two-electron processes in the mutual neutralization of O- with O+ and N+ at Subthermal Collision Energies

We have measured total absolute cross sections for the Mutual Neutralization (MN) of O- with O+/N+. A fine resolution (of about 50 meV) in the kinetic energy spectra of the product neutral atoms allows unique identification of the atomic states participating in the mutual neutralization process. Cross sections and branching ratios have also been calculated down to 1 meV center-of-mass collision energy for these two systems with a multi-channel Landau-Zener model and an asymptotic method for the ionic-covalent coupling matrix elements. The importance of two-electron processes in one-electron transfer is demonstrated by the dominant contribution of a core-excited configuration of the nitrogen atom in N+ + O- collisions. This effect is partially accounted for by introducing configuration mixing in the evaluation of coupling matrix elements.Comment: 5 pages, 4 figure

Failure of hydrogenation in protecting polycyclic aromatic hydrocarbons from fragmentation

A recent study of soft X-ray absorption in native and hydrogenated coronene cations, C$_{24}$H$_{12+m}^+$ $m=0-7$, led to the conclusion that additional hydrogen atoms protect (interstellar) Polycyclic Aromatic Hydrocarbon (PAH) molecules from fragmentation [Reitsma et al., Phys. Rev. Lett. 113, 053002 (2014)]. The present experiment with collisions between fast (30-200 eV) He atoms and pyrene (C$_{16}$H$_{10+m}^+$, $m=0$, 6, and 16) and simulations without reference to the excitation method suggests the opposite. We find that the absolute carbon-backbone fragmentation cross section does not decrease but increases with the degree of hydrogenation for pyrene molecules.Comment: 10 pages, 5 figure