684 research outputs found
Detection of low-velocity impact-induced delaminations in composite laminates using Auto-Regressive models
In this paper, the detection of delaminations in carbon-fiber-reinforced-plastic (CFRP) laminate plates induced by low-velocity impacts (LVI) is investigated by means of Auto-Regressive (AR) models obtained from the time histories of the acquired responses of the composite specimens. A couple of piezoelectric patches for actuation and sensing purposes are employed. The proposed structural health monitoring (SHM) routine begins with the selection of the suitable locations of the piezoelectric transducers via the numerical analysis of the curvature mode shapes of the CFRP plates. The normalized data recorded for the undamaged plate configuration are then analyzed to obtain the most suitable AR model using five techniques based on the Akaike Information Criterion (AIC), the Akaike Final Prediction Error (FPE), the Partial Autocorrelation Function (PAF), the Root Mean Squared (RMS) of the AR residuals for different order p, and the Singular Value Decomposition (SVD). Linear Discriminant Analysis (LDA) is then applied on the AR model parameters to enhance the performance of the proposed delamination identification routine. Results show the effectiveness of the developed procedure when a reduced number of sensors is available
flavour symmetries as Peccei-Quinn symmetries
We investigate to what extent a generic, generation-dependent symmetry
acting on the quark Yukawa operators can reduce the number of free parameters
by forcing some entries in the Yukawa matrices to vanish. The maximal reduction
compatible with CP violation yields nine real parameters and one phase, which
matches the number of physical observables, implying that such models have no
free parameters. We derive a set of results: (i) the only possible structures
have the form , where the subscripts indicate the number of
real parameters in the Yukawa matrices, (ii) there are only two inequivalent
Yukawa structures, each one giving rise to six different models depending on
quark flavour assignments, (iii) the symmetries that generate these
textures all have a QCD anomaly, and hence are Peccei-Quinn symmetries,
reinforcing the idea of a possible connection between the quark flavour puzzle
and the axion solution to the strong CP problem, (iv) in some cases the
contributions to the QCD anomaly of two generations cancels out, and this opens
the possibility that the axion coupling to nucleons could be strongly
suppressed. Flavour-violating axion couplings to quarks are completely fixed,
up to the axion decay constant, providing a non-trivial complementarity between
low-energy flavour-violating processes and standard axion searches.Comment: v2: version accepted for publication in JHEP; figure 1 updated; minor
additions; 23 pages, 1 figure. v1: 20 pages, 1 figur
Interactive semantic mapping: Experimental evaluation
Robots that are launched in the consumer market need to provide more effective human robot interaction, and, in particular, spoken language interfaces. However, in order to support the execution of high level commands as they are specified in natural language, a semantic map is required. Such a map is a representation that enables the robot to ground the commands into the actual places and objects located in the environment. In this paper, we present the experimental evaluation of a system specifically designed to build semantically rich maps, through the interaction with the user. The results of the experiments not only provide the basis for a discussion of the features of the proposed approach, but also highlight the manifold issues that arise in the evaluation of semantic mapping
A Proposal for Semantic Map Representation and Evaluation
Semantic mapping is the incremental process of “mapping” relevant information of the world (i.e., spatial information, temporal events, agents and actions) to a formal description supported by a reasoning engine. Current research focuses on learning the semantic of environments based on their spatial location, geometry and appearance. Many methods to tackle this problem have been proposed, but the lack of a uniform representation, as well as standard benchmarking suites, prevents their direct comparison. In this paper, we propose a standardization in the representation of semantic maps, by defining an easily extensible formalism to be used on top of metric maps of the environments. Based on this, we describe the procedure to build a dataset (based on real sensor data) for benchmarking semantic mapping techniques, also hypothesizing some possible evaluation metrics. Nevertheless, by providing a tool for the construction of a semantic map ground truth, we aim at the contribution of the scientific community in acquiring data for populating the dataset
Knowledge Representation for Robots through Human-Robot Interaction
The representation of the knowledge needed by a robot to perform complex
tasks is restricted by the limitations of perception. One possible way of
overcoming this situation and designing "knowledgeable" robots is to rely on
the interaction with the user. We propose a multi-modal interaction framework
that allows to effectively acquire knowledge about the environment where the
robot operates. In particular, in this paper we present a rich representation
framework that can be automatically built from the metric map annotated with
the indications provided by the user. Such a representation, allows then the
robot to ground complex referential expressions for motion commands and to
devise topological navigation plans to achieve the target locations.Comment: Knowledge Representation and Reasoning in Robotics Workshop at ICLP
201
The landscape of QCD axion models
We review the landscape of QCD axion models. Theoretical constructions that
extend the window for the axion mass and couplings beyond conventional regions
are highlighted and classified. Bounds from cosmology, astrophysics and
experimental searches are reexamined and updated.Comment: Review article for Physics Reports, 151 pages. Few typos and signs
corrected. Matches journal versio
An experimental investigation on mass failures occurring in a riverbank composed of sandy gravel
Higher order terms of Mather's -function for symplectic and outer billiards
We compute explicitly the higher order terms of the formal Taylor expansion
of Mather's -function for symplectic and outer billiards in a
strictly-convex planar domain . In particular, we specify the third terms of
the asymptotic expansions of the distance (in the sense of the symmetric
difference metric) between and its best approximating inscribed or
circumscribed polygons with at most vertices. We use tools from affine
differential geometry.Comment: 17 pages, 3 figure
Window for preferred axion models
We discuss phenomenological criteria for defining “axion windows,” namely regions in the parameter space of the axion-photon coupling where realistic models live. Currently, the boundaries of this region depend on somewhat arbitrary criteria, and it would be highly desirable to specify them in terms of precise phenomenological requirements. We first focus on hadronic axion models within post-inflationary scenarios, in which the initial abundance of the new vectorlike quarks Q is thermal. We classify their representations R Q by requiring that (i) the Q are sufficiently short lived to avoid issues with long-lived strongly interacting relics, (ii) the theory remains weakly coupled up to the Planck scale. The more general case of multiple R Q is also studied, and the absolute upper and lower bounds on the axion-photon coupling as a function of the axion mass is identified. Pre-inflationary scenarios in which the axion decay constant remains bounded as f a ≤ 5 × 10 11     GeV allow for axion-photon couplings only about 20% larger. Realistic Dine-Fischler-Srednicki-Zhitnitsky type of axion models also remain encompassed within the hadronic axion window. Some mechanisms that can allow to enhance the axion-photon coupling to values sizeably above the preferred window are discussed
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