Optimal Node Visitation in Acyclic Stochastic Digraphs with Multi-threaded Traversals and Internal Visitation Requirements

The original definition of the problem of optimal node visitation (ONV) in acyclic stochastic digraphs concerns the identification of a routing policy that will enable the visitation of each leaf node a requested number of times, while minimizing the expected number of the graph traversals. The original work of Bountourelis and Reveliotis (2006) formulated this problem as a Stochastic Shortest Path (SSP) problem, and since the state space of this SSP formulation is exponentially sized with respect to the number of the target nodes, it also proposed a suboptimal policy that is computationally tractable and asymptotically optimal. This paper extends the results of Bountourelis and Reveliotis (2006) to the cases where (i) the tokens traversing the graph can “split” during certain transitions to a number of (sub-)tokens, allowing, thus, the satisfaction of many visitation requirements during a single graph traversal, and (ii) there are additional visitation requirements attached to the internal graph nodes, which, however, can be served only when the visitation requirements of their successors have been fully met. In addition, the presented set of results establishes stronger convergence properties for the proposed suboptimal policies, and it provides a formal complexity analysis of the considered ONV formulations. From a practical standpoint, the extension of the original results performed in this paper enables their effective usage in the application domains that motivated the ONV problem, in the first place.

Optimal scheduling of contract algorithms with soft deadlines

A contract algorithm is an algorithm which is given, as part of its input, a specified amount of allowable computation time, and may not return useful results if interrupted prior to that time. In contrast, an interruptible algorithm will always output some meaningful (albeit suboptimal) solution, even if interrupted during its execution. Simulating interruptible algorithms by means of schedules of executions of contract algorithms in parallel processors is a well-studied problem with significant applications in AI. In the standard model, the interruptions are hard deadlines in which a solution must be reported immediately at the time the interruption occurs. In this paper, we study the more general setting of scheduling contract algorithms in the presence of soft deadlines. In particular, we address the setting in which if an interruption occurs at time t, then the system is given an additional window of time \(w(t)\le c \cdot t\), for constant c, within which the simulation must be completed. We formulate extensions to performance measures of schedules under this setting and derive schedules of optimal performance for all concave functions w.     

An empirical investigation of the effects of firm characteristics on the propensity to adopt cloud computing

Cloud computing (CC) is emerging as a new paradigm of resource acquisition and management of information and communication technologies (ICT) by firms, which can offer significant benefits, but at the same time can pose significant risks as well, so its adoption by firms has been lower than the initial expectations. Therefore, it is quite important to gain a better understanding of the factors affecting positively or negatively the adoption of CC. This paper presents an empirical investigation of the effects on a firm’s propensity to adopt CC of a set of firm characteristics referring to technological infrastructure, strategy, personnel skills, size and competition. Its conceptual foundation is the Technology, Organization and Environment theory of technological innovation adoption. Our study is based on data from 676 European manufacturing firms from the glass, ceramics and cement sectors, which have been collected through the e-Business Survey of the European Commission. The results indicate that in the above sectors ICT infrastructure sophistication has the strongest positive effect on CC adoption propensity among all examined firm characteristics. Furthermore, we have found that the existence of an ICT investment reduction strategy, the employment of specialized ICT personnel and the existence of previous experience of ICT outsourcing also have positive effects on a firm’s propensity to adopt CC. On the contrary, employees ICT skills, price and quality competition do not affect CC adoption propensity. Finally, our results also indicate that in the three examined sectors firm size has no significant influence on the propensity to adopt CC.     

Cyberbullying‐Entrenched or Cyberbully‐Free Classrooms? A Class Network and Class Composition Approach

Cyberbullying threatens young people's well‐being. This study is one of the first to examine cyberbullying from a social network perspective. The class‐based friendship networks of 103 classes were reconstructed using peer‐nomination questionnaires. Closeness centralization and the global clustering coefficient were calculated using social network analysis and subsequently entered into a Poisson‐regression. The outcomes of these analyses show that in classes featured by high closeness centralization in the offline and online friendship network, more cyberbullying happens. Additionally, our analyses reveal that in classes featuring a high global clustering coefficient in the online network, less cyberbullying occurs. The composition of the class in terms of gender and ethnicity were not significantly associated with the number of cyberbullying incidents in class.     

Path Planning and Control of a Cooperative Three-Robot System Manipulating Large Objects

After a brief review of the current research on multi-robot systems, the paper presents a path planning and control scheme for a cooperative three-robot system transferring/manipulating a large object from an initial to a desired final position/orientation. The robots are assumed to be capable of holding the object at three points that define an isosceles triangle. The mode of operation adopted is that of a master-and-two-slave robots. The control scheme employs the differential displacement of the object which is transformed into that of the end-effector of each robotic arm, and then used to compute the differential displacements of the joints of the robots. The scheme was applied to several 3-robot systems by simulation and proved to be adequately effective, subject to certain conditions regarding the magnitude of the differential displacements. Here, an example is included which concerns the case of three Stäubli RX-90L robots.     

Initial use of 1-hydroxybenzotriazole in the chemistry of group 12 metals: An 1D zinc(II) coordination polymer and a mononuclear cadmium(II) complex containing the deprotonated ligand in a novel monodentate ligation mode

The chemistry of 1-hydroxybenzotriazole (btaOH) with the group 12 metal ions Zn(II) and Cd(II) resulted in the 1D coordination polymer [Zn(btaO)₂]_n (1) and the mononuclear complex [Cd(btaO)₂(H₂O)₄] · 3H₂O (2 · 3H₂O), respectively. Polymer 1 forms double-stranded chains which are further supported by weak C–H?O hydrogen bonds resulting in a pcu (primitive cubic) rod packing. The mononuclear complexes of 2 form undulating hydrogen bonded layers while the lattice water molecules form 1D hydrogen bonded tapes, comprising 4- and 6-membered rings, within the layers and bridge them to the third dimension. The thermal and optical properties of both compounds are presented. IR data are discussed in terms of the chemical composition of the compounds and the coordination mode of btaO^?.     

The Application and Evaluation of Banker''s Algorithm for Deadlock-Free Buffer Space Allocation in Flexible Manufacturing Systems

Deadlock-free operation is essential for operating highly automated manufacturing systems. The seminal deadlock avoidance procedure, Banker's algorithm, was developed for computer operating systems, an environment where very little information regarding the future resource requirements of executing processes is known. Manufacturing researchers have tended to dismiss Banker's algorithm as too conservative in the manufacturing environment where future resource requirements are well defined by part routes. In this work, we investigate this issue by developing variants of Banker's algorithm applicable to buffer space allocation in flexible manufacturing. We show that these algorithms are not overly conservative and that, indeed, Banker's approach can provide very good operational flexibility when properly applied to the manufacturing environment.