738 research outputs found

    A special class of solutions in F(R)F(R)-gravity

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    We consider a special class of vacuum F(R)F(R)-modified gravity models. The form of their Lagrangian is such that the field equations are trivially satisfied when the Ricci scalar is constant. There are many interesting F(R)F(R)-models for inflation and dark energy that fall in this class. However, little is known outside the domain of cosmology therefore we aim to explore the class of solutions that are static and spherically symmetric. After some general considerations, we investigate in more detail black hole solutions, traversable wormhole metrics and, finally, configurations that can match the anomalous rotation curves of galaxies.Comment: Minor typos corrected, references added. Version accepted for publication in the European Physical Journal

    A simple method for pile-up correction by high-speed nanoindentation combined with optical profilometry

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    focused ion beam and nanomechanical tests for high resolution surface characterisation new resources for platinum group metals testing

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    *Email: [email protected] Recently, the increasing importance and scope of nanotechnology has extended the need for high resolution characterisation tools beyond their traditional domains. As a consequence, advanced high-resolution tools at the nanoscale are now increasingly used in research and development (RD and nanoindentation testing. After a brief description of both techniques (architecture, probe-sample interaction basics and operation modes), the effectiveness of this combined approach is demonstrated for microstructural and nanomechanical investigations on very small samples. The advantages are low cost, fast and site-specific sample preparation for transition electron microscopy (TEM) analysis; study of the mechanical hardening effect on microstructure and hardness profile at the micron scale; failure analysis; and understanding of plasticity and elasticity behaviour. Two specific case studies related to a platinum-copper alloy for jewellery use and a platinum-rhodium alloy for sensor manufacturing are presented and discussed

    A class of static spherically symmetric solutions in f(T)f(T)-gravity

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    We study a class of static spherically symmetric vacuum solutions in modified teleparallel gravity solving the field equations for a specific model Ansatz, requiring the torsion scalar TT to be constant. We discuss the models falling in this class. After some general considerations, we provide and investigate local solutions in the form of black holes and traversable wormholes as well as configurations that can match the anomalous rotation curves of galaxies

    Robust Bayes classifiers

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    AbstractNaive Bayes classifiers provide an efficient and scalable approach to supervised classification problems. When some entries in the training set are missing, methods exist to learn these classifiers under some assumptions about the pattern of missing data. Unfortunately, reliable information about the pattern of missing data may be not readily available and recent experimental results show that the enforcement of an incorrect assumption about the pattern of missing data produces a dramatic decrease in accuracy of the classifier. This paper introduces a Robust Bayes Classifier (rbc) able to handle incomplete databases with no assumption about the pattern of missing data. In order to avoid assumptions, the rbc bounds all the possible probability estimates within intervals using a specialized estimation method. These intervals are then used to classify new cases by computing intervals on the posterior probability distributions over the classes given a new case and by ranking the intervals according to some criteria. We provide two scoring methods to rank intervals and a decision theoretic approach to trade off the risk of an erroneous classification and the choice of not classifying unequivocally a case. This decision theoretic approach can also be used to assess the opportunity of adopting assumptions about the pattern of missing data. The proposed approach is evaluated on twenty publicly available databases

    A class of static spherically symmetric solutions in f(Q)f(Q)-gravity

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    We analyze a class of topological static spherically symmetric vacuum solutions in f(Q)f(Q)-gravity. We considered an Ansatz ensuring that those solutions trivially satisfy the field equations of the theory when the non-metricity scalar is constant. In the specific, we provide and discuss local solutions in the form of black holes and traversable wormholes.Comment: 12 pages, 0 figure

    Cluster Generation and Cluster Labelling for Web Snippets: A Fast and Accurate Hierarchical Solution

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    This paper describes Armil, a meta-search engine that groups into disjoint labelled clusters the Web snippets returned by auxiliary search engines. The cluster labels generated by Armil provide the user with a compact guide to assessing the relevance of each cluster to her information need. Strik- ing the right balance between running time and cluster well- formedness was a key point in the design of our system. Both the clustering and the labelling tasks are performed on the ?y by processing only the snippets provided by the auxil- iary search engines, and use no external sources of knowl- edge. Clustering is performed by means of a fast version of the furthest-point-?rst algorithm for metric k-center cluster- ing. Cluster labelling is achieved by combining intra-cluster and inter-cluster term extraction based on a variant of the information gain measure. We have tested the clustering ef- fectiveness of Armil against Vivisimo, the de facto industrial standard in Web snippet clustering, using as benchmark a comprehensive set of snippets obtained from the Open Di- rectory Project hierarchy. According to two widely accepted external\u27 metrics of clustering quality, Armil achieves bet- ter performance levels by 10%. We also report the results of a thorough user evaluation of both the clustering and the cluster labelling algorithms. On a standard 1GHz ma- chine, Armil performs clustering and labelling altogether in less than one second

    Residual stress assessment on polymers and composites by focused ion beam microscale Ring-core method

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    The aim of this project is to analyze locally the residual stress of a polymer-matrix composite of industrial relevance by using a novel focused ion beam (FIB) method. The project approach is to solve the problem of the analysis of a polymeric base material displaying high electrical resistivity, since the focused ion beam (FIB) microscope is nowadays only useful for conductive materials. Based on the results obtained future possible uses are determined in the biomedical field, such as: intramedullary nails, bone plates, screws, rods, etc
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