660 research outputs found

    How Many Cooks Spoil the Soup ?

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    On the Transformation Capability of Feasible Mechanisms for Programmable Matter

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    We study theoretical models of programmable matter systems, consisting of n spherical modules kept together by magnetic or electrostatic forces and able to perform two minimal mechanical operations (movements): rotate and/or slide. The goal is for an initial shape A to transform to some target shape B by a sequence of movements. Most of the paper focuses on transformability (feasibility) questions. When only rotation is available, we prove that deciding whether two given shapes can transform to each other, is in P. Under the additional restriction of maintaining global connectivity, we prove inclusion in PSPACE and explore minimum seeds that can make otherwise infeasible transformations feasible. Allowing both rotations and slidings yields universality: any two connected shapes of the same order can be transformed to each other without breaking connectivity, in O(n2) sequential and O(n) parallel time (both optimal). We finally provide a type of distributed transformation

    Connectivity Preserving Network Transformers

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    The Population Protocol model is a distributed model that concerns systems of very weak computational entities that cannot control the way they interact. The model of Network Constructors is a variant of Population Protocols capable of (algorithmically) constructing abstract networks. Both models are characterized by a fundamental inability to terminate. In this work, we investigate the minimal strengthenings of the latter that could overcome this inability. Our main conclusion is that initial connectivity of the communication topology combined with the ability of the protocol to transform the communication topology plus a few other local and realistic assumptions are sufficient to guarantee not only termination but also the maximum computational power that one can hope for in this family of models. The technique is to transform any initial connected topology to a less symmetric and detectable topology without ever breaking its connectivity during the transformation. The target topology of all of our transformers is the spanning line and we call Terminating Line Transformation the corresponding problem. We first study the case in which there is a pre-elected unique leader and give a time-optimal protocol for Terminating Line Transformation. We then prove that dropping the leader without additional assumptions leads to a strong impossibility result. In an attempt to overcome this, we equip the nodes with the ability to tell, during their pairwise interactions, whether they have at least one neighbor in common. Interestingly, it turns out that this local and realistic mechanism is sufficient to make the problem solvable. In particular, we give a very efficient protocol that solves Terminating Line Transformation when all nodes are initially identical. The latter implies that the model computes with termination any symmetric predicate computable by a Turing Machine of space Θ(n2)\Theta(n^2)

    Terminating Distributed Construction of Shapes and Patterns in a Fair Solution of Automata

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    In this work, we consider a solution of automata (or nodes) that move passively in a well-mixed solution without being capable of controlling their movement. Nodes can cooperate by interacting in pairs and every such interaction may result in an update of their local states. Additionally, the nodes may also choose to connect to each other in order to start forming some required structure. Such nodes can be thought of as small programmable pieces of matter, like tiny nanorobots or programmable molecules. The model that we introduce here is a more applied version of network constructors, imposing physical (or geometric) constraints on the connections that the nodes are allowed to form. Each node can connect to other nodes only via a very limited number of local ports. Connections are always made at unit distance and are perpendicular to connections of neighboring ports, which makes the model capable of forming 2D or 3D shapes. We provide direct constructors for some basic shape construction problems, like spanning line, spanning square, and self-replication. We then develop new techniques for determining the computational and constructive capabilities of our model. One of the main novelties of our approach is that of exploiting the assumptions that the system is well-mixed and has a unique leader, in order to give terminating protocols that are correct with high probability. This allows us to develop terminating subroutines that can be sequentially composed to form larger modular protocols. One of our main results is a terminating protocol counting the size n of the system with high probability. We then use this protocol as a subroutine in order to develop our universal constructors, establishing that it is possible for the nodes to become self-organized with high probability into arbitrarily complex shapes while still detecting termination of the construction

    Social Media Use For Work: Does Work Experience Really Matter?

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    Social media are in the top of the agenda for many companies to date, however there seems to be very limited understanding of the usage of social media for work purposes. In this study, we investigate what values increase this usage, and whether that usage is related with employees’ performance. Additionally, we explore the impact of employees’ work experience on their social media behaviour. Our study is based on responses from 1799 employees in the insurance industry. Results confirmed that both utilitarian and hedonic values influence employees to use more social media for their work. In addition, this study confirms that there is an important relation between the use of social media and work performance. Last but not least, employees’ work experience is found to be a significant moderator of the relationship between social media use for work and work performance

    How Many Cooks Spoil the Soup?

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    In this work, we study the following basic question: "How much parallelism does a distributed task permit?" Our definition of parallelism (or symmetry) here is not in terms of speed, but in terms of identical roles that processes have at the same time in the execution. We initiate this study in population protocols, a very simple model that not only allows for a straightforward definition of what a role is, but also encloses the challenge of isolating the properties that are due to the protocol from those that are due to the adversary scheduler, who controls the interactions between the processes. We (i) give a partial characterization of the set of predicates on input assignments that can be stably computed with maximum symmetry, i.e., Θ(Nmin)\Theta(N_{min}), where NminN_{min} is the minimum multiplicity of a state in the initial configuration, and (ii) we turn our attention to the remaining predicates and prove a strong impossibility result for the parity predicate: the inherent symmetry of any protocol that stably computes it is upper bounded by a constant that depends on the size of the protocol.Comment: 19 page

    Temporal Network Optimization Subject to Connectivity Constraints

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    In this work we consider temporal networks, i.e. networks defined by a labeling λ assigning to each edge of an underlying graph G a set of discrete time-labels. The labels of an edge, which are natural numbers, indicate the discrete time moments at which the edge is available. We focus on path problems of temporal networks. In particular, we consider time-respecting paths, i.e. paths whose edges are assigned by λ a strictly increasing sequence of labels. We begin by giving two efficient algorithms for computing shortest time-respecting paths on a temporal network. We then prove that there is a natural analogue of Menger’s theorem holding for arbitrary temporal networks. Finally, we propose two cost minimization parameters for temporal network design. One is the temporality of G, in which the goal is to minimize the maximum number of labels of an edge, and the other is the temporal cost of G, in which the goal is to minimize the total number of labels used. Optimization of these parameters is performed subject to some connectivity constraint. We prove several lower and upper bounds for the temporality and the temporal cost of some very basic graph families such as rings, directed acyclic graphs, and trees

    A MATTER OF TRUST AND EMOTIONS: A COMPLEXITY THEORY APPROACH TO EXPLAIN THE ADOPTION OF EGOVERNMENT SERVICES

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    This research uses complexity theory to offer a deeper insight on the causal patterns of factors explaining the adoption of e-government services. To this end, we propose a conceptual model comprising of affective factors (positive and negative emotions) and cognitive factors (trust of the government, trust of the service, and perceived net benefits of e-government services) along with research propositions. Our propositions are validated by employing a fuzzy-set qualitative comparative analysis (fsQCA) on a sample of 502 users of e-government services. Findings indicate five configurations of cognitive and affective perceptions that lead to high intention to use an e-government service. Of paramount importance are affective values and trust values since their mandatory presence or absence is incorporated in all configurations. The study has both theoretical and practical implications for academic scholars pertaining the development of new e-government adoption theories and the provision of egovernment services

    Fuzzy-Set Analysis to Understand User Experience in Mobile Applications

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    This paper examines how price value, game content quality, positive and negative emotions, gender, and gameplay time interact with each other to explain high intention to download mobile applications, and specifically mobile games. Based on complexity theory and theory of configuration, a conceptual model is drawn along with research propositions. We employ fuzzy-set qualitative comparative analysis (fsQCA) on 531 users of mobile games, and identify ten solutions that explain high intention to download mobile games. Alternative paths are presented depending on the gender and gameplay time. We highlight the importance of price value and game content quality, as well as that of positive emotions which are always core factors when present. We contributes to theory and practice (1) with new insights into the interrelationships among the predictors of user intention to download mobile games, and (2) by advancing the theoretical and methodological foundation of how these predictors combine to lead to high intention to download mobile games
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