11 research outputs found

    Πρόβλεψη του ρυθμού προχώρησης μηχανών ολομέτωπης κοπής (ΤΒΜ) με τη χρήση τεχνητών νευρωνικών δικτύων

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    Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Σχεδιασμός και Κατασκευή Υπόγειων Έργων

    Scalable Communication Cost Reduction: The Chord Case

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    In peer-to-peer (P2P) network system design a main focus is on efficient service discovery schemes, most frequently assuming permanent (or long-term stationary) positions for service facilities, neglecting communication costs due to the actual locations of the facilities. Since the problem of communication cost minimization is a large optimization problem (NP-hard) and requires global information (i.e., not scalable), in this paper the service migration philosophy is adopted which permits service facility movements and yields smaller communication cost in a scalable manner (i.e., based on local information). Service migration is incorporated in the Chord P2P system, imposing certain changes (e.g., the extension of the service discovery scheme of Chord) and introducing an extra system overhead (i.e., update messages) for the efficient operation of the (enhanced) system. As it is demonstrated here using simulation results, the communication cost corresponding to the extra system overhead is significantly small and more than enough compensated for by the communication cost reduction due to the introduction of service migration. As long as the network remains unchanged, the former communication cost is paid only once while the latter communication cost reduction is permanent

    Fully Persistent B-Trees

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    We present I/O-efficient fully persistent B-Trees that support range searches at any version in O(logB n + t/B) I/Os and updates at any version in O(logB n + log2 B) amortized I/Os, using space O(m/B) disk blocks. By n we denote the number of elements in the accessed version, by m the total number of updates, by t the size of the query’s output, and by B the disk block size. The result improves the previous fully persistent B-Trees of Lanka and Mays by a factor of O(logB m) for the range query complexity and O(logB n) for the update complexity. To achieve the result, we first present a new B-Tree implementation that supports searches and updates in O(logB n) I/Os, using O(n/B) blocks of space. Moreover, every update makes in the worst case a constant number of modifications to the data structure. We make these B-Trees fully persistent using an I/O-efficient method for full persistence that is inspired by the nodesplitting method of Driscoll et al. The method we present is interesting in its own right and can be applied to any external memory pointer based data structure with maximum in-degree din bounded by a constant and out-degree bounded by O(B), where every node occupies a constant number of blocks on disk. The I/O-overhead per modification to the ephemeral structure is O(din log2 B) amortized I/Os, and the space overhead is O(din/B) amortized blocks. Access to a field of an ephemeral block is supported in O(log2 din) worst case I/Os.

    Combinatorial GVNS (General Variable Neighborhood Search) Optimization for Dynamic Garbage Collection

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    General variable neighborhood search (GVNS) is a well known and widely used metaheuristic for efficiently solving many NP-hard combinatorial optimization problems. We propose a novel extension of the conventional GVNS. Our approach incorporates ideas and techniques from the field of quantum computation during the shaking phase. The travelling salesman problem (TSP) is a well known NP-hard problem which has broadly been used for modelling many real life routing cases. As a consequence, TSP can be used as a basis for modelling and finding routes via the Global Positioning System (GPS). In this paper, we examine the potential use of this method for the GPS system of garbage trucks. Specifically, we provide a thorough presentation of our method accompanied with extensive computational results. The experimental data accumulated on a plethora of TSP instances, which are shown in a series of figures and tables, allow us to conclude that the novel GVNS algorithm can provide an efficient solution for this type of geographical problem

    Will Fly Repellency Using Deltamethrin Reduce Intramammary Infections, Stress and Fatigue Indicators of Dairy Ewes under Intensive Management?

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    Intramammary infections (IMIs) caused by various pathogens may lead to clinical or subclinical mastitis, challenging the health and welfare status of infected animals and decreasing the quantity and quality of the produced milk. Additionally, the zoonotic potential of some of the pathogens isolated from IMI cases, the emergence of antibiotic resistance due to the extensive antibiotic use for IMI treatment, and the accumulation of antibiotic residues in milk and meat represent significant concerns for public health. Therefore, the investigation of IMI risk factors and the proposal of efficient measures to mitigate their effects on animal health and welfare is crucial. Although fly infestation is considered to play a significant role in the transmission of IMI pathogens, its adverse effects on udder health and the overall comfort status of dairy ewes have not been quantified and assessed on an evidential basis. Hence, the objectives of this study were to assess, for the first time, the fly repellent effect of deltamethrin and link it to: (i) the occurrence of common bacterial IMI; (ii) the somatic cell counts in milk; and (iii) the serum cortisol and creatine kinase levels (stress and fatigue indicators). The study was carried out in an intensive dairy sheep farm in northern Greece, during peak fly season. Deltamethrin treatment was associated with a reduced (i) number of flies (mostly Musca domestica) landing on treated ewes, compared to untreated ones (p aureus Staphylococci IMIs (p p p < 0.001), indicating a less stressful environment for them

    Isolation of Listeria monocytogenes from poultry red mite (Dermanyssus gallinae) infesting a backyard chicken farm in Greece

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    Abstract The poultry red mite (PRM), Dermanyssus gallinae, is arguably the most harmful, ubiquitous haematophagous ectoparasite infesting egg-laying hens. PRM is a vector of various microorganisms, with some being important for food microbiology and public health. The present study aimed to investigate the presence of specific pathogens, including Escherichia coli, Salmonella spp. and Listeria spp., carried by PRM infesting a chicken farm in Greece. Mites were caught using cardboard traps (Avivet), and 100 unwashed PRM were homogenized and used for microbiological cultures. Microbiological cultures were carried out on general and selective substrates to detect the above-mentioned bacteria. Specifically for Listeria spp., DNA was extracted from bacteria grown in Tryptone Soya Yeast Extract Agar using a commercial kit. The hly gene encoding the Listeriolysin O protein was amplified by PCR. Mites were identified as D. gallinae using morphological keys as well as by COI DNA barcoding. Microbiological cultures and PCR assays were positive for Listeria monocytogenes. No other bacteria were detected. The current study constitutes the first molecular isolation of L. monocytogenes from D. gallinae, confirming that PRM can carry this food-borne pathogen. PRM control measures and hygiene practices should be applied to minimize any possible contamination risk of poultry products with L. monocytogenes and safeguard public health