A Tight Lower Bound on the Controllability of Networks with Multiple Leaders

In this paper we study the controllability of networked systems with static network topologies using tools from algebraic graph theory. Each agent in the network acts in a decentralized fashion by updating its state in accordance with a nearest-neighbor averaging rule, known as the consensus dynamics. In order to control the system, external control inputs are injected into the so called leader nodes, and the influence is propagated throughout the network. Our main result is a tight topological lower bound on the rank of the controllability matrix for such systems with arbitrary network topologies and possibly multiple leaders

Resilience of Locally Routed Network Flows: More Capacity is Not Always Better

In this paper, we are concerned with the resilience of locally routed network flows with finite link capacities. In this setting, an external inflow is injected to the so-called origin nodes. The total inflow arriving at each node is routed locally such that none of the outgoing links are overloaded unless the node receives an inflow greater than its total outgoing capacity. A link irreversibly fails if it is overloaded or if there is no operational link in its immediate downstream to carry its flow. For such systems, resilience is defined as the minimum amount of reduction in the link capacities that would result in the failure of all the outgoing links of an origin node. We show that such networks do not necessarily become more resilient as additional capacity is built in the network. Moreover, when the external inflow does not exceed the network capacity, selective reductions of capacity at certain links can actually help averting the cascading failures, without requiring any change in the local routing policies. This is an attractive feature as it is often easier in practice to reduce the available capacity of some critical links than to add physical capacity or to alter routing policies, e.g., when such policies are determined by social behavior, as in the case of road traffic networks. The results can thus be used for real-time monitoring of distance-to-failure in such networks and devising a feasible course of actions to avert systemic failures.Comment: Accepted to the IEEE Conference on Decision and Control (CDC), 201

A Message Passing Strategy for Decentralized Connectivity Maintenance in Agent Removal

In a multi-agent system, agents coordinate to achieve global tasks through local communications. Coordination usually requires sufficient information flow, which is usually depicted by the connectivity of the communication network. In a networked system, removal of some agents may cause a disconnection. In order to maintain connectivity in agent removal, one can design a robust network topology that tolerates a finite number of agent losses, and/or develop a control strategy that recovers connectivity. This paper proposes a decentralized control scheme based on a sequence of replacements, each of which occurs between an agent and one of its immediate neighbors. The replacements always end with an agent, whose relocation does not cause a disconnection. We show that such an agent can be reached by a local rule utilizing only some local information available in agents' immediate neighborhoods. As such, the proposed message passing strategy guarantees the connectivity maintenance in arbitrary agent removal. Furthermore, we significantly improve the optimality of the proposed scheme by incorporating $\delta$-criticality (i.e. the criticality of an agent in its $\delta$-neighborhood).Comment: 9 pages, 9 figure

Determination of Mechanical Properties of Concrete by Destructive and Non-Destructive Experimental Methods

This paper examines the mechanical quality differences of concrete by destructive and non destructive methods according to shape, dimension relationship and cure conditions. Within destructive methods, (compression, tension, bending) different shaped-sized concretes and 28-days-old concrete shear wall samples tested along to find modulus of elasticity. Non destructive methods (ultrasonic pulse velocity test, rebound hammer test) applied same samples along to determine compressive strength and longitudinal wave velocity to obtain result of modulus of elasticity. The aim was to achieve data from applied laboratory test results and cross-checking, all values to enhance concretes compressive strength for potential possibilities

Image based visual servoing using algebraic curves applied to shape alignment

Visual servoing schemes generally employ various image features (points, lines, moments etc.) in their control formulation. This paper presents a novel method for using boundary information in visual servoing. Object boundaries are modeled by algebraic equations and decomposed as a unique sum of product of lines. We propose that these lines can be used to extract useful features for visual servoing purposes. In this paper, intersection of these lines are used as point features in visual servoing. Simulations are performed with a 6 DOF Puma 560 robot using Matlab Robotics Toolbox for the alignment of a free-form object. Also, experiments are realized with a 2 DOF SCARA direct drive robot. Both simulation and experimental results are quite promising and show potential of our new method

Izvanbolnička istodobna operacija ventralne i preponske hernije u lokalnoj anesteziji: prikaz slučaja

Umbilical and epigastric hernias are occasionally seen in patients with groin hernias, however, there is almost no published evidence about their simultaneous repair. In a 3-year period, 10 patients were subjected to simultaneous repair of groin hernias (7 unilateral, 2 bilateral inguinal and 1 femoral) and ventral hernias (7 primary, 2 recurrent umbilical and 1 epigastric) with local infiltration anesthesia and intravenous sedation. The mean total bupivacaine dose was 18 (10- 30) mL and mean total lidocaine dose 21 (14-30) mL. The mean time to resuming normal daily activity was 5.5 days, whereas the time to car driving was 3-7 days. The oral analgesic (naproxen sodium) requirement was 6-10 tablets for 3-5 days. Patient acceptance was excellent. Simultaneous repair of groin and ventral hernias with local anesthesia in outpatient setting is feasible and associated with a low complication rate and maximum patient comfort.Umbilikalne i epigastrične hernije ponekad se nalaze u bolesnika s preponskom hernijom, međutim, gotovo da nema objavljenih podataka o njihovom istodobnom operacijskom liječenju. Tijekom 3-godišnjeg razdoblja istodobna operacija preponskih hernija (7 jednostranih, 2 obostrane ingvinalne i 1 femoralna) i ventralnih hernija (7 primarnih i 2 opetovane umbilikalne i 1 epigastrična) u lokalnoj infiltracijskoj anesteziji i intravenskoj sedaciji izvedena je u 10 bolesnika. Srednja ukupna doza bupivakaina bila je 10 (10-30) mL, a srednja ukupna doza lidokaina 21 (14-30) mL. Srednje vrijeme do povratka normalnih svakodnevnih aktivnosti bilo je 5,5 dana, a za upravljanje motornih vozilima 3-7 dana. Potreba za oralnim analgeticima (naproksen natrij) bila je 6-10 tableta kroz 3-5 dana. Bolesnici su izvrsno prihvatili ove zahvate. Istodobno rješavanje preponske i ventralne hernije uz lokalnu anesteziju u izvanbolničkim uvjetima izvedivo je, ima nisku stopu komplikacija i najvišu razinu udobnosti za bolesnika