1,721,114 research outputs found
Caratterizzazione sedimentologica, produzione carbonatica e fattori di controllo dei substrati colonizzati da praterie a fanerogame marine nel Mediterraneo Occidentale
No full textSono state studiate le caratteristiche granulometriche e composizionali dei sedimenti associati a sette praterie della fanerogama Posidonia oceanica ubicate nel Mediterraneo occidentale, quattro nel mar Tirreno, due in Sardegna occidentale ed una in Corsica occidentale, per poterne riconoscere le attuali facies sedimentarie, utili anche per la ricostruzione paleoambientale della zona fotica nel record fossile. I posidonieti studiati presentano settori delle praterie sviluppati sia su sabbia che su roccia, oltreché formanti la caratteristica struttura definita "matte". Le praterie investigate si trovano in aree caratterizzate, tra loro, da diverse caratteristiche fisiografiche, oceanografiche e morfologiche; da diversi apporti terrigeni, derivanti sia da erosione costiera che da apporti fluviali. Sono state individuate cinque facies sedimentarie, da quella puramente terrigena a quella prettamente bioclastica: sabbie e ghiaie terrigene (con le subfacies sabbie terrigene e sabbie ghiaiose terrigene), sabbie bioclastiche, sabbie ghiaiose, sabbie miste carbonatiche-terrigene e sabbie terrigene più o meno classate (con le due subfacies sabbie terrigene moderatamente classate e sabbie terrigene ben classate). Tutte le cinque facies associate alla P. oceanica si sviluppano nel campo della sabbia, la frazione ghiaiosa è generalmente subordinata e di entità variabile e la frazione fangosa (silt e argilla) è quasi sempre molto bassa. La scarsezza di sedimento fangoso può essere attribuita a processi di risospensione e/o alla mancanza di produzione di tali granulometrie. In due posidonieti tra quelli studiati, il tasso di produzione carbonatica epifitica, non soltanto fogliare, è stato stimato in 400 g m-2 anno-1. Le aliquote di carbonato derivanti dalla produzione epifitica e dalla componente scheletrica (gusci carbonatici) degli organismi viventi associati alle praterie di P. oceanica, vanno a contribuire alla formazione del caratteristico mixing di sedimenti carbonatici-silicoclastici associati all’ambiente costiero poco profondo del Mediterraneo. La produzione carbonatica associata alle praterie di fanerogame temperate, come quelle della P. oceanica, danno associazioni del tipo heterozoan, con la componente photozoan assente o subordinata. Le associazioni sono dominate da gusci di tipo calcitico e la maggior parte della produzione carbonatica è data da organismi eterotrofi, non dipendenti dalla luce ma la stretta relazione tra organismi produttori e fanerogame, viste come substrati di crescita o zone di ricovero, limita le facies sedimentarie alla zona eufotica, e ciò va tenuto in forte considerazione per una corretta ricostruzione paloeambientale in caso di analisi di record fossili. La componente scheletrica di molti organismi associati alle praterie di fanerogame contribuisce fortemente alla formazione dei sedimenti carbonatici della zona fotica degli ambienti marini di acqua poco profonda; infine, le praterie di fanerogame giocano un ruolo sostanziale per la produzione di carbonati e per il sequestro di carbonio, organico ed inorganico, durante il Cenozoico
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
Automatic evaluation of form errors
No full textAutomating completely the process of geometric
errors verification has some problems. The most criti-cal ones are the preventive shape recognition and the
lack of an agreement about criteria to be used to
associate ideal features to the extracted points from
the real surface.
In this paper an approach for automatic metrologi-cal inspection of manufactured parts is proposed.
Starting from a tessellated model, coming from a
scanned workpiece, the methodology carries out
automatically the partition of the acquired surface by
a shape recognition approach. Then, the ideal featu-res are associated to the corresponding non-ideal fea-tures, based on some criteria that permit to define the
minimum zone solution. The proposed methodology
stands out for the number and the types of the auto-matically recognized features. Finally, the form
errors, related to all the recognized features, are eva-luated.
In this paper the procedure has been used to eva-luate some specific form error typologies for several
simulated case-studies and real objects. The results
deriving from this experimentation are here critically
discussed
Recognition of intrinsic quality properties for automatic geometric inspection
Full text linkIn the last few years the need for methodologies capable of performing an automated geometric inspection has increased. These methodologies often use 3D high-resolution optical digitisers to acquire points from the surface of the object to be inspected. It is expected that, in the near future, geometric inspection will be requiring more and more the use of these instruments. At present geometric inspection is not profiting from all the opportunities attainable by 3D high-resolution optical scanners or from the numerous tools which can be used for processing the point cloud acquired from the inspected product. For some years now, these authors have been working on a new methodology for automatic tolerance inspection working from a 3D model acquired by optical digitisers. In this paper all the information recognisable in a scanned object is organised into a new data structure, called Recognised Geometric Model (RGM). The final aim is to define a representation of the inspected object for the automatic evaluation of the non-idealities pertaining to the form, orientation and location of the non-ideal features of the acquired object. The key concept of the proposed approach is the capability to recognise some intrinsic nominal properties of the acquired model. These properties are assumed as references to evaluate the non-idealities of the inspected object. With this approach the references of geometric inspection are searched for in the inspected object independently of a tolerance specification and of the availability of a 3D nominal representation. The high-level geometric information within RGM depends on the rules used for its identification. The capability to recognise specific categories of nominal references offers the possibility of introducing new tolerances to be specified. The proposed approach has been implemented in original software by means of which a specific test case has been analysed
Automatic error evaluation of axial-symmetric surfaces
No full textThis paper aims at developing a suitable analysis of the point cloud, coming from the optic
scanning of a real object, allowing to evaluate automatically the errors without using a nominal
CAD model or a GPS specification. Really, this possibility is strictly depending on the capability
to recognize in a scanned tessellated model some intrinsic nominal references. This paper is
particularly devoted to the automatic error evaluation of axial – symmetric surfaces; for this kind
of surfaces two types of intrinsic references can be recognized. An original classification of the
error categories is proposed and the related methods for the evaluation of these errors are
presented. The methodology is applied to some real cases and the related results are critically
discussed
Fuzzy sets for geometric shape recognition in triangular meshes
No full textShape recognition of geometric models described by triangular meshes is affected by some problems which made it difficult
to be performed without errors. Some factors, such as the location errors of points due to acquisition process and the coarse
representation of continuous surfaces due to triangular approximation, introduce uncertainty in the recognition process of
the geometric shape. This paper introduces some original fuzzy sets suited to recognize geometric form. The membership
functions of the fuzzy sets are dynamically defined so that they can be adapted to take into account those properties of the
geometric model that affect the uncertainty of the recognition process. The proposed approach is intrinsically very robust
and achieves good results also in recognising form features in geometric models affected by point location errors
Fuzzy sets for geometric shape recognition in triangular meshes
Full text linkShape recognition of geometric models described
by triangular meshes is aected by some problems
which made it dicult to be performed without er-
rors. Some factors, such as the location errors of
points due to acquisition process and the coarse rep-
resentation of continuous surfaces due to triangular
approximation, introduce uncertainty in the recogni-
tion process of the geometric shape. This paper in-
troduces some original fuzzy sets suited to recognize
geometric form. The membership functions of the
fuzzy sets are dynamically dened so that they can
be adapted to take into account those properties of
the geometric model that aect the uncertainty of
the recognition process. The proposed approach is
intrinsically very robust and achieves good results
also in recognising form features in geometric mod-
els aected by point location errors
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