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

Kombinatorikus Optimalizálás: Algoritmusok, Strukturák, Alkalmazások = Combinatorial optimization: algorithms, structures, applications

Mint azt az OTKA-pályázat munkaterve tartalmazza, a pályázatban résztvevő kutatók alkotják a témavezető irányításával működő Egerváry Jenő Kombinatorikus Optimalizálási Kutatócsoportot. A csoport a kutatási tervben szereplő több témában jelentős eredményeket ért el az elmúlt 4 évben, ezekről a pályázat résztvevőinek több mint 50 folyóiratcikke jelent meg, és számos rangos nemzetközi konferencián ismertetésre kerültek. Néhány kiemelendő eredmény: sikerült polinomiális kombinatorikus algoritmust adni irányított gráf pont-összefüggőségének növelésére; jelentős előrelépés történt a háromdimenziós térben merev gráfok jellemzésével és a molekuláris sejtéssel kapcsolatban; 2 dimenzióban sikerült bizonyítani Hendrickson sejtését; a párosításelméletben egy újdonságnak számító módszerrel számos új algoritmikus eredmény született; több, gráfok élösszefüggőségét jellemző tételt sikerült hipergráfokra általánosítani. | As the research plan indicates, the researchers participating in the project are the members of the Egerváry Research Group, led by the coordinator. The group has made important progress in the past 4 years in the research topics declared in the research plan. The results have been published in more than 50 journal papers, and have been presented at several prestigious international conferences. The most significant results are the following: a polynomial algorithm has been found for the node-connectivity augmentation problem of directed graphs; considerable progress has been made towards the characterization of 3-dimensional rigid graphs and towards the proof of the molecular conjecture; Hendrickson's conjecture has been proved in 2 dimensions; several new algorithmic results were obtained in matching theory using a novel approach; several theorems characterizing connectivity properties of graphs have been generalized to hypergraphs

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

Physical modelling of chemical compaction, overpressure development, hydraulic fracturing and thrust detachments in organic-rich source rock

International audienceGeological evidence for overpressure is common worldwide, especially in petroleum-rich sedimentary basins. As a result of an increasing emphasis on unconventional resources, new data are becoming available for source rocks. Abnormally high values of pore fluid pressure are especially common within mature source rock, probably as a result of chemical compaction and increases in volume during hydrocarbon generation. To investigate processes of chemical compaction, overpressure development and hydraulic fracturing, we have developed new techniques of physical modelling in a closed system. During the early stages of our work, we built and deformed models in a small rectangular box (40 40 10 cm), which rested on an electric flatbed heater; but more recently, in order to accommodate large amounts of horizontal shortening, we used a wider box (77 75 10 cm). Models consisted of horizontal layers of two materials: (1) a mixture of equal initial volumes of silica powder and beeswax micro-spheres, representing source rock, and (2) pure silica powder, representing overburden. By submerging these materials in water, we avoided the high surface tensions, which otherwise develop within pores containing both air and liquids. Also we were able to measure pore fluid pressure in a model well. During heating, the basal temperature of the model surpassed the melting point of beeswax (w62 C), reaching a maximum of 90 C. To investigate tectonic contexts of compression or extension, we used a piston to apply horizontal displacements. In experiments where the piston was static, rapid melting led to vertical compaction of the source layer, under the weight of overburden, and to high fluid overpressure (lithostatic or greater). Crosssections of the models, after cooling, revealed that molten wax had migrated through pore space and into open hydraulic fractures (sills). Most of these sills were horizontal and their roofs bulged upwards, as far as the free surface, presumably in response to internal overpressure and loss of strength of the mixture.We also found that sills were less numerous towards the sides of the box, presumably as a result of boundary effects. In other experiments, in which the piston moved inward, causing compression of the model, sills also formed. However, these were thicker than in static models and some of them were subject to folding or faulting. For experiments, in which we imposed some horizontal shortening, before the wax had started to melt, fore-thrusts and back-thrusts developed across all of the layers near the piston, producing a high-angle prism. In contrast, as soon as the wax melted, overpressure developed within the source layer and a basal detachment appeared beneath it. As a result, thin-skinned thrusts propagated further into the model, producing a low-angle prism. In some experiments, bodies of wax formed imbricate zones within the source layer. Thus, in these experiments, it was the transformation, from solid wax to liquid wax, which led to chemical compaction, overpressure development and hydraulic fracturing, all within a closed system. According to the measurements of overpressure, load transfer was the main mechanism, but volume changes also contributed, producing supra-lithostatic overpressure and therefore tensile failure of the mixture

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

Verification of State/Event Systems by Quotienting

A rather new approach towards compositional verification of concurrent systems is the quotient technique, where components are gradually removed from the concurrent system while transforming the specification accordingly. When the intermediate specifications can be kept small using heuristics for minimization, the state explosion problemis avoided and there are already promising experimental results for systems with an interleaving semantics, including real-time systems. This paper extends the quotienting approach to deal with a synchronous framework in the shape of state/event systems. A state/event system is a concurrent system with a set of interdependent components operating synchronously according to stimuli (input events) provided by an environment while producing output events in return for the environment. A compositional modal logic M suitable for expressing general safety and liveness properties subsystems is introduced. A quotient construction for building components from a state/event system into the specification is presented and heuristics for minimizing formulae are proposed. The techniques are demonstrated on an example. The correctness of the techniques are justified by proofs in an appendix

Characterising fracture systems within upfaulted basement highs in the Hebridean Islands: an onshore analogue for the Clair Field

The Outer Hebrides are a structurally complex area, comprised predominantly of crystalline basement rocks of the Lewisian Gneiss Complex with the multiply reactivated Outer Hebrides Fault Zone following eastern portions of the islands for over 200 km along strike. In Eastern Lewis, the Permo-Triassic Stornoway Formation unconformably overlies Lewisian basement rocks of the OHFZ in a half-graben. This structural setting is analogous to the major offshore Clair oil field, where oil is found within Devonian-Carboniferous red beds of the Clair Group directly overlying Lewisian Gneiss Complex rocks of the Rona Ridge, which was upfaulted in the Mesozoic. Oil connection and flow has been proven in the basement rocks at Clair, however, little is known about the nature of fracturing and faulting within the basement and how these faults link to the cover sequence. Here, the cover and basement rocks of the Outer Hebridean Islands of Lewis and Harris are studied as an analogue. Faults, fault rocks and deformation are characterised within the Stornoway Formation, and at the basement-cover interface, allowing recognition of Mesozoic and younger faults within the Lewisian and their separation from older structures. Three fault sets are distinguished within the Stornoway Formation: a NNW-SSE striking normal fault set (Set 1); a N-S and E-W quadrimodal normal fault set (Set 2); and a less numerous late E-W strike-slip set (Set 3). Tertiary dolerite dyke intrusion occurred along Set 1 and Set 2 faults prior to the formation of Set 3. Palaeostress analyses reveal that Set 1 and 2 result from E-W and ENE-WSW directed extension vectors, followed by E-W directed contraction associated with Set 3. These orientations are interpreted to be representative of Mesozoic extension related to the opening of the Atlantic, followed by Cenozoic contraction. Faults in the Stornoway Formation are accompanied by development of authigenic clay-bearing gouges and cataclasites, ± calcite cement and late zeolite. Zeolite is often associated with secondary porosity, produced through dissolution of calcite. Mesozoic and younger faults are readily identified in Lewisian Gneiss rocks of the Stornoway region based on fault rock characterisation, and these faults also display an ENE-WSW directed extension vector. The major bounding faults of the Stornoway Formation are sub-parallel with the local foliation and the reactivation of the basement foliation by Mesozoic faults is proven. Fault trends identified within the Stornoway Formation are also sub-parallel with the local foliation. Conjugate faulting apparent in the Stornoway Formation is not present within the Lewisian, possibly indicating a degree of structural detachment between faulting in the basement and faulting in the cover, probably linked to the development of low-angle faults within the Stornoway Formation within metres of and parallel with the basement-cover unconformity. The basement-cover interface displays abundant evidence of fluid overpressure, potentially linked with dewatering during lithification and local fault movements. Mesozoic and younger-age brittle fault rocks post-date pre-existing extensive ductile and brittle deformation that are most intense within the OHFZ. Brittle fault rocks of pre-Mesozoic age are associated with pseudotachylites, fine grained cataclasites, epidote-bearing cataclasites and pumpellyite-bearing cataclasites. Mesozoic fault rocks contain authigenic clay-bearing gouges and cataclasites often associated with zeolite and adularia mineralisation that often accompanies the development of secondary porosity within the fault rocks. This chronological fault rock assemblage represents the continued exhumation of the islands after the successively lower temperature and pressures conditions experienced since the initial development of the basement gneiss complex. Across Lewis, fault rock characterisation allows identification of major Mesozoic and younger structures that cross the islands, with a km-scale offset postulated across the major Seaforth Fault that may link the major NE-SW striking Minch Fault to a NE-SW striking fault lying offshore western Lewis/Harris. On Lewis, the predominant orientation of Mesozoic structures is NNW-SSE, becoming NW-SE on Harris, south of the Seaforth Fault and where foliation becomes pervasively NW-SE. It seems highly likely that, as identified in the Stornoway Region, the foliation orientation plays a significant role in the development of later structures. At Clair, fault rock development within the Devonian-Carboniferous Clair Group is dependent on the host lithology, with gouges formed in mudstones, and granulation seams found in porous, oil-bearing sandstones. Calcite-cemented breccias are present in zones of calcite cemented host rock. Pyrite and calcite vein mineralisation are associated with oil influx, and a late phase of dissolution was accompanied by faulting that produced uncemented brittle fault rocks (gouge). In the basement, oil is seen along open fractures and in vug-like secondary porosity associated with adularia mineralisation, of which two forms are present. Euhedral adularia is often altered to green clay and partially to wholly infills tensile fractures that may predate the emplacement of the Clair Group. Later adularia occurs as ‘speckled’ veins, with haematite, clay, calcite, pyrite, minor zeolite and oil, and appears to be contemporaneous with calcite-pyrite veining (i.e. Mesozoic in age). Porosity in both adularia-bearing fractures is associated with oil staining. The basement displays little evidence of extensive mylonites or phyllonites that are obvious in the OHFZ of the Outer Hebrides. Scalability studies show that it is difficult to assign power-law spacing distributions to fractures within the basement rocks of the Hebrides. Fractures parallel with Mesozoic structures do however tend to display a greater degree of organisation with more clustering of fractures as the faults are approached. Mesozoic fault-perpendicular fracture sets display more strongly random fracture spacing distributions consistent with a jointing origin. At Clair, fracture spacing studies in the cover show a low fracture density compared to basement, with fracture spacing that is clustered and may be well represented by power-laws. Dissolution has locally produced a randomly spaced fracture network. Although fracture spacings in the Hebridean Lewisian are generally random, fracture apertures define a clear power law relationship over ~5 orders of magnitude. Similarly, results from the Clair group also display equivalent power law relationships

Insights into Rockfall from Constant 4D Monitoring

Current understanding of the nature of rockfall and their controls stems from the capabilities of slope monitoring. These capabilities are fundamentally limited by the frequency and resolution of data that can be captured. Various assumptions have therefore arisen, including that the mechanisms that underlie rockfall are instantaneous. Clustering of rockfall across rock faces and sequencing through time have been observed, sometimes with an increase in pre-failure deformation and pre-failure rockfall activity prior to catastrophic failure. An inherent uncertainty, however, lies in whether the behaviour of rockfall monitored over much shorter time intervals (Tint) is consistent with that previously monitored at monthly intervals, including observed failure mechanisms, their response to external drivers, and pre-failure deformation. To address the limitations of previous studies on this topic, 8 987 terrestrial laser scans have been acquired over 10 months from continuous near-real time monitoring of an actively failing coastal rock slope (Tint = 0.5 h). A workflow has been devised that automatically resolves depth changes at the surface to 0.03 m. This workflow filters points with high positional uncertainty and detects change in 3D, with both approaches tailored to natural rock faces, which commonly feature sharp edges and partially occluded areas. Analysis of the resulting rockfall inventory, which includes > 180 000 detachments, shows that the proportion of rockfall < 0.1 m3 increases with more frequent surveys for Tint < ca. 100 h, but this trend does not continue for surface comparison over longer time intervals. Therefore, and advantageously, less frequent surveys will derive the same rockfall magnitude-frequency distribution if captured at ca. 100 h intervals as compared to one month or even longer intervals. The shape and size of detachments shows that they are more shallow and smaller than observable rock mass structure, but appear to be limited in size and extent by jointing. Previously explored relationships between rockfall timing and environmental and marine conditions do not appear to apply to this inventory, however, significant relationships between rockfall and rainfall, temperature gradient and tides are demonstrated over short timescales. Pre-failure deformation and rockfall activity is observed in the footprint of incipient rockfall. Rockfall activity occurs predominantly within the same ca. 100 h timescale observed in the size-distribution analysis, and accelerated deformation is common for the largest rockfall during the final 2 h before block detachment. This study provides insights into the nature and development of rockfall during the period prior to detachment, and the controls upon it. This holds considerable implications for our understanding of rockfall and the improvement of future rockfall monitoring

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