On Heterogeneous Covert Networks

Covert organizations are constantly faced with a tradeoff between secrecy and operational efficiency. Lindelauf, Borm and Hamers (2008) developed a theoretical framework to deter- mine optimal homogeneous networks taking the above mentioned considerations explicitly into account. In this paper this framework is put to the test by applying it to the 2002 Jemaah Islamiyah Bali bombing. It is found that most aspects of this covert network can be explained by the theoretical framework. Some interactions however provide a higher risk to the network than others. The theoretical framework on covert networks is extended to accommodate for such heterogeneous interactions. Given a network structure the optimal location of one risky interaction is established. It is shown that the pair of individuals in the organization that should conduct the interaction that presents the highest risk to the organization, is the pair that is the least connected to the remainder of the network. Furthermore, optimal networks given a single risky interaction are approximated and compared. When choosing among a path, star and ring graph it is found that for low order graphs the path graph is best. When increasing the order of graphs under consideration a transition occurs such that the star graph becomes best. It is found that the higher the risk a single interaction presents to the covert network the later this transition from path to star graph occurs.covert networks;terrorist networks;heterogeneity;game theory;information;secrecy

Understanding Terrorist Network Topologies and Their Resilience Against Disruption

This article investigates the structural position of covert (terrorist or criminal) networks. Using the secrecy versus information tradeoff characterization of covert networks it is shown that their network structures are generally not small-worlds, in contradistinction to many overt social networks. This finding is backed by empirical evidence concerning Jemaah Islamiyah's Bali bombing and a heroin distribution network in New York. The importance of this finding lies in the strength such a topology provides. Disruption and attack by counterterrorist agencies often focuses on the isolation and capture of highly connected individuals. The remarkable result is that these covert networks are well suited against such targeted attacks as shown by the resilience properties of secrecy versus information balanced networks. This provides an explanation of the survival of global terrorist networks and food for thought on counterterrorism strategy policy.terror networks;terrorist cells;network structure;counterterrorism

The Influence of Secrecy on the Communication Structure of Covert Networks

In order to be able to devise successful strategies for destabilizing terrorist organizations it is vital to recognize and understand their structural properties. This paper deals with the opti- mal communication structure of terrorist organizations when considering the tradeoff between secrecy and operational efficiency. We use elements from game theory and graph theory to determine the `optimal' communication structure a covert network should adopt. Every covert organization faces the constant dilemma of staying secret and ensuring the necessary coordina- tion between its members. For several different secrecy and information scenarios this dilemma is modeled as a game theoretic bargaining problem over the set of connected graphs of given order. Assuming uniform exposure probability of individuals in the network we show that the Nash bargaining solution corresponds to either a network with a central individual (the star graph) or an all-to-all network (the complete graph) depending on the link detection probabil- ity, which is the probability that communication between individuals will be detected. If the probability that an individual is exposed as member of the network depends on the information hierarchy determined by the structure of the graph, the Nash bargaining solution corresponds to cellular-like networks.covert networks;terrorist networks;Nash bargaining;game theory;information;secrecy

One-Mode Projection Analysis and Design of Covert Affiliation Networks

Subject classifications: Terrorism; Counterinsurgency; Intelligence; Defense; Covert networks; Affiliation networks.

Charge Dynamics at the Silicon(001) Surface Studied by Scanning Tunneling Microscopy and Surface Photovoltage

Scanning tunneling microscopy measurements of local surface photovoltage of the Si(001) surface reveal the existence of local charging produced by the tunneling current. Since the tunneling current is confined to a region of near atomic dimensions, charge transport between surface and bulk electronic states is probed with high spatial resolution. The surface charge is enhanced while tunneling at the bonded, type-B atomic step and at specific point defects demonstrating atomic-scale variations in the charge dynamics

Understanding Terrorist Network Topologies and Their Resilience Against Disruption

This article investigates the structural position of covert (terrorist or criminal) networks. Using the secrecy versus information tradeoff characterization of covert networks it is shown that their network structures are generally not small-worlds, in contradistinction to many overt social networks. This finding is backed by empirical evidence concerning Jemaah Islamiyah's Bali bombing and a heroin distribution network in New York. The importance of this finding lies in the strength such a topology provides. Disruption and attack by counterterrorist agencies often focuses on the isolation and capture of highly connected individuals. The remarkable result is that these covert networks are well suited against such targeted attacks as shown by the resilience properties of secrecy versus information balanced networks. This provides an explanation of the survival of global terrorist networks and food for thought on counterterrorism strategy policy.

Theoretical study of isolated dangling bonds, dangling bond wires and dangling bond clusters on H:Si(100)-(2×\times1) surface

We theoretically study the electronic band structure of isolated unpaired and paired dangling bonds (DB), DB wires and DB clusters on H:Si(100)-(2$\times$1) surface using Extended H\"uckel Theory (EHT) and report their effect on the Si band gap. An isolated unpaired DB introduces a near-midgap state, whereas a paired DB leads to $\pi$ and $\pi^*$ states, similar to those introduced by an unpassivated asymmetric dimer (AD) Si(100)-(2$\times$1) surface. Such induced states have very small dispersion due to their isolation from the other states, which reside in conduction and valence band. On the other hand, the surface state induced due to an unpaired DB wire in the direction along the dimer row (referred to as $[\bar{1}10]$), has large dispersion due to the strong coupling between the adjacent DBs, being 3.84$\AA$ apart. However, in the direction perpendicular to the dimer row (referred to as [110]), due to the reduced coupling between the DBs being 7.68$\AA$ apart, the dispersion in the surface state is similar to that of an isolated unpaired DB. Apart from this, a paired DB wire in $[\bar{1}10]$ direction introduces $\pi$ and $\pi^*$ states similar to those of an AD surface and a paired DB wire in [110] direction exhibits surface states similar to those of an isolated paired DB, as expected. Besides this, we report the electronic structure of different DB clusters, which exhibit states inside the band gap that can be interpreted as superpositions of states due to unpaired and paired DBs.Comment: 7 pages, 10 figure, 1 tabl

Discourje: Runtime verification of communication protocols in clojure

This paper presents Discourje: a runtime verification framework for communication protocols in Clojure. Discourje guarantees safety of protocol implementations relative to specifications, based on an expressive new version of multiparty session types. The framework has a formal foundation and is itself implemented in Clojure to offer a seamless specification–implementation experience. Benchmarks show Discourje’s overhead can be less than 5% for real/existing concurrent programs