Route Swarm: Wireless Network Optimization through Mobility

In this paper, we demonstrate a novel hybrid architecture for coordinating networked robots in sensing and information routing applications. The proposed INformation and Sensing driven PhysIcally REconfigurable robotic network (INSPIRE), consists of a Physical Control Plane (PCP) which commands agent position, and an Information Control Plane (ICP) which regulates information flow towards communication/sensing objectives. We describe an instantiation where a mobile robotic network is dynamically reconfigured to ensure high quality routes between static wireless nodes, which act as source/destination pairs for information flow. The ICP commands the robots towards evenly distributed inter-flow allocations, with intra-flow configurations that maximize route quality. The PCP then guides the robots via potential-based control to reconfigure according to ICP commands. This formulation, deemed Route Swarm, decouples information flow and physical control, generating a feedback between routing and sensing needs and robotic configuration. We demonstrate our propositions through simulation under a realistic wireless network regime.Comment: 9 pages, 4 figures, submitted to the IEEE International Conference on Intelligent Robots and Systems (IROS) 201

Structured Connectivity Augmentation

We initiate the algorithmic study of the following "structured augmentation" question: is it possible to increase the connectivity of a given graph G by superposing it with another given graph H? More precisely, graph F is the superposition of G and H with respect to injective mapping phi:V(H)->V(G) if every edge uv of F is either an edge of G, or phi^{-1}(u)phi^{-1}(v) is an edge of H. Thus F contains both G and H as subgraphs, and the edge set of F is the union of the edge sets of G and phi(H). We consider the following optimization problem. Given graphs G, H, and a weight function omega assigning non-negative weights to pairs of vertices of V(G), the task is to find phi of minimum weight omega(phi)=sum_{xyin E(H)}omega(phi(x)phi(y)) such that the edge connectivity of the superposition F of G and H with respect to phi is higher than the edge connectivity of G. Our main result is the following ``dichotomy\u27\u27 complexity classification. We say that a class of graphs C has bounded vertex-cover number, if there is a constant t depending on C only such that the vertex-cover number of every graph from C does not exceed t. We show that for every class of graphs C with bounded vertex-cover number, the problems of superposing into a connected graph F and to 2-edge connected graph F, are solvable in polynomial time when Hin C. On the other hand, for any hereditary class C with unbounded vertex-cover number, both problems are NP-hard when Hin C. For the unweighted variants of structured augmentation problems, i.e. the problems where the task is to identify whether there is a superposition of graphs of required connectivity, we provide necessary and sufficient combinatorial conditions on the existence of such superpositions. These conditions imply polynomial time algorithms solving the unweighted variants of the problems

A detachment algorithm for inferring a graph from path frequency

Abstract: Inferring graphs from path frequency has been studied as an important problem which has a potential application to drug design and elucidation of chemical structures. Given a multiple set g of strings of labels with length at most K, the problem asks to find a vertex-labeled graph G that attains a one-to-one correspondence between g and the occurrences of labels along all paths of length at most K in G. In this paper, we prove that the problem with K = 1 can be formulated as a problem of finding a loopless and connected detachment, based on which an efficient algorithm for solving the problem is derived. Our algorithm also solves the problem with an additional constraint such that every vertex in an inferred graph is required to have a specified degree

What is a ‘Good’ Encoding of Guarded Choice?

The pi-calculus with synchronous output and mixed-guarded choices is strictly more expressive than the pi-calculus with asynchronous output and no choice. This result was recently proved by Palamidessi and, as a corollary, she showed that there is no fully compositional encoding from the former into the latter that preserves divergence-freedom and symmetries. This paper argues that there are nevertheless `good' encodings between these calculi. In detail, we present a series of encodings for languages with (1) input-guarded choice, (2) both input- and output-guarded choice, and (3) mixed-guarded choice, and investigate them with respect to compositionality and divergence-freedom. The first and second encoding satisfy all of the above criteria, but various `good' candidates for the third encoding - inspired by an existing distributed implementation - invalidate one or the other criterion. While essentially confirming Palamidessi's result, our study suggests that the combination of strong compositionality and divergence-freedom is too strong for more practical purposes

Decoding Choice Encodings

We study two encodings of the asynchronous pi-calculus with input-guarded choice into its choice-free fragment. One encoding is divergence-free, but refines the atomic commitment of choice into gradual commitment. The other preserves atomicity, but introduces divergence. The divergent encoding is fully abstract with respect to weak bisimulation, but the more natural divergence-free encoding is not. Instead, we show that it is fully abstract with respect to coupled simulation, a slightly coarser - but still coinductively defined - equivalence that does not enforce bisimilarity of internal branching decisions. The correctness proofs for the two choice encodings introduce a novel proof technique exploiting the properties of explicit decodings from translations to source terms

Three dimensional geophysical modeling : from physics to numerical simulation

The main object of this thesis is to provide a comprehensive numerical tool for the three-dimensional simulation of sedimentary basins. Sedimentary basins, in particular salt basins, are the best places to find oil, natural gas and to store dangerous nuclear waste material. The low permeability of salt guarantees low water leakage which is the main concern for the safety of a nuclear waste storage. For this reason one of the best places for a nuclear waste depository is a salt mine. These two applications call for a thorough knowledge of the basin evolution on geological time scales. Until now sedimentary basin studies have been based mainly on geological interpretation: experienced specialists estimate the history of a basin on the basis of common knowledge. More often, they provide a list of possible scenarios. An appropriate numerical simulator can provide the right tool to choose, among these scenarios, the correct one or, at least, the most realistic

Constitutive Modelling for Sedimentary Evolution at Basin Scale

This work is focused on the development of constitutive models for elastoplastic-fracture behaviour in scenarios characterised by large deformation ranging from laboratory to geolog-ical length scale. Both seepage and geomechanical fields are considered, with the assumption of isothermal field.The standard Drucker-Prager model is enhanced by applying π-plane correction factor, and the use of hardening properties which depends on the evolution of effective plastic strain. Non-associative potential plastic flow function is used to derive the plastic flow vector. To ensure finite energy dissipation during softening, regularisation technique based on fracture energy approach is adopted. The resulting modified Drucker-Prager model is combined with rotating crack model (which relies on Rankine failure criterion) to develop an elastoplastic-fracture framework by considering multi-step stress update procedures. The advantage of multi-step stress update is that the framework allows the use of any elastoplastic model without any major change in the code. Performance of this set of constitutive models is assessed by studying several simulation examples, including bearing capacity of strip footing, crack propagation in a specimen with pre-existing inclined fault, influence of size effect on borehole instability, influence of pore pressure on thrust fault formation, and hydraulic fracture due to fluid injection. Overall, the numerical results show good agreement with available analytical solutions or experimental findings.For basin-scale problem, SR4 model is used due to its capability to capture the evolution of pre-consolidation pressure pc, that is not considered in Drucker-Prager model. In this case, the goal is to simulate basin-scale gravitational deformation in a prograding delta due to fluid overpressure in shale layer with synkinematic sedimentation. With the aid of adaptive remeshing algorithm, the result successfully produces distinct fault patterns across the prograding delta in terms of plastic strain distribution. In particular, three different zones are observed: extensional, transition, and compressional zone. The extensional zone is characterised by basinward-dipping normal faults, whereas the compressional zone is characterised by basinward-verging fore-thrust faults.Overall, the simulation results illustrate the potential that the developed constitutive models under the integrated flow-geomechanical modelling framework could offer to future analysis of more complex geological evolution