1,721,082 research outputs found
Vision-Based State Estimation of an Uncooperative Space Object
No full textAutomation is widely applied for classical robotics application but is still underexploited in space missions. However, autonomous operations would be extremely advantageous in this field, with a wide range of possible applications. One of the most relevant topic in this context is autonomous relative navigation around unknown and uncooperative objects. In the past, several different approaches have been proposed to solve this problem. This paper wants to investigate the potentiality of an hybrid approach, combining image processing techniques for pose estimation with robust filtering methods. A first estimate of the pose of the observed uncooperative object is provided by the image processing step on monocular camera images. The Vision Based navigation algorithm, developed at PoliMi, works detecting salient features from the incoming images, given by the monocamera; among these, the ones corresponding to the uncooperative object are matched to an already available on-board map (constituted by a 3D point cloud correlated with descriptors from real images), in this way a set of 3D to 2D correspondences is obtained. The set of correspondences is then used to solve the so called Perspective-n-Point problem (PnP), which gives as result a first estimate of the relative position of the camera (and hence of the target-chaser) which is expressed in terms of rototranslation. Motion only Bundle Adjustment, is then applied for pose optimization. The estimate of the pose is fed to the navigation filter. Relative translation and rotation are considered decoupled without any loss of generality. A linear model that accounts for eccentricity is implemented and used as model of the dynamics inside the filter. The use of a linear model allows for the exploitation of robust Kalman filter techniques. For the rotational dynamics, the non-linear equations constrain to use a non-linear filter such as the Extended Kalman Filter. However, the use of an alternative formulation, based on Lie-Groups, is here investigated. A first numerical validation of the filter is presented by using, as input, measurements obtained from synthetic images. Moreover, preliminary description of a future experimental validation of the complete algorithm is presented. A Mistubishi PA-10 robotic arm is used to replicate the relative motion of the target satellite. A realistic 3D-printed mock-up of a satellite is installed on the robotic arm end-effector. A single fixed camera acquires images of the moving mock-up
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The pre-lymphatic pathway, the rooths of the lymphatic system in breast tissue: a 3D study.
No full textThe pre-lymphatic pathway, the rooths of the lymphatic system in breast tissue: a 3D study
No full textThree-dimensional (3D) visualisation of microscopic structures provides useful information about their configuration and the spatial (hence functional) relationship between different components in tissues.
This paper describes 3D dynamic reconstructions of the pre-lymphatic labyrinth in two cases of "normal" breast core biopsies and one case of pseudoangiomatous stromal hyperplasia. Direct anastomoses between pre-lymphatic channels and
true lymphatics of the breast were demonstrated. It is concluded that pre-lymphatics are a way of communication between breast epithelial/stromal structures and the main lymphatic system. The
present findings suggest that the existence of prelymphatics
has to be taken in consideration in the intramammary spread of malignant tumours
Glass-made adjustable integration mold for x-ray optics: Experimental feasibility campaign
No full textCold Slumping Glass Optics is a cost-effective technique to realize segmented X-ray optics. It is based on the replica approach: very thin flat glass foils are shaped to theoretical form by means of integration molds and fixed into stacks by means of ribs. As the theoretical shape of each of the layer depends on the radius of curvature inside the assembly, in principle different integration molds are needed to realize a stack. A worthwhile solution would be the usage of a single adjustable mold with and 'optical surface' to be shaped according to the position of the plate in the stack. The selection of the optical surface material and the bending strategy are the most relevant points. Glass would give major benefits in terms of thermal coupling with the glass foils, scratch resistance during operations and costs. On the other hand, given the reduced bending capability of the material coupled with its intrinsic fragility, experimental tests are necessary to assess the feasibility of the solution. In this paper we present the design and the implementation study as realized by the PoliMI-DAER. An experimental test campaign has been carried out beside the theoretical studies, to validate numerical models and obtain feedbacks from an early implementation. The test campaign is expounded along with the analysis of the results. A preliminary comparison with the numerical simulations is given
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