1,721,037 research outputs found
Prediction Models of Inertial Particle Transport Using a Combined Lattice Boltzmann - Immersed Boundary Method
Full text linkLow Reynolds number flows involve different fields of technical interest, such as flows confined to very small section ducts, or generally flows involving small geometries, such as those of interest in the biomedical field; or flows for which viscous forces have a dominant role as in the case of lubrication problems.
At very small scales the distance between the molecules constituting the fluid becomes comparable to the cha-racteristic size of the problem, so that their mutual behavior, in terms of collisions, has to be modelled. At this scales and low Reynolds flows, the continuos model described by Navier-Stokes equation can become inadequate, where instead the so called mesoscopic approach is justified. It is placed in an intermediate position between the molecular dynamics, and the description based on the continuous fluid of the Navier-Stokes equations. The model based on the Boltzmann equation provides a mesoscopic approach based on a probability density function, commonly called distribution function.The model can describe non-stationary flows at scales of interest in the biological field.
The numerical method used to solve the boltzmann equation for the problems on which the work is focused is the Lattice-Boltzmann Method (LBM), and a parallel three-dimensional code for the simulation of low Reynolds number flows was developed and tested.
The unsteady problem of technological interest is the transport of nanoparticles and microparticles, it involves the study of the fluid structure interaction over time. An Immersed Boundary (IB) method was implemented into the code to simulate the presence of bodies surrounded by the flow. and is used to compute the hydrodynamic stresses acting on an immersed rigid or deformable particle. The combined Lattice Boltzmann-Immersed Boundary method represents a good compromise between accuracy and computational burden into the simulation of rigid and deformable moving particles. The fluid–structure interaction has often been investigated through kinetic models, in which the immersed particles motion depends only on the velocity field surrounding them, the peculiar novelty and improvement of this work is to consider a dynamic fluid–structure interaction method, for which the motion is solved considering the hydrodynamics forces exchanged through the body boundaries.
A set of other models are selected to simulate the deformation of the particles and the adhesion phenomena and behaviour in walls proximity. This allows the study of several biomedical cases with the accuracy that some physical phenomena require
New investigations on the Protoaurignacian lithic technology of Fumane cave.
No full textThe Aurignacian has always been considered an unquestionable cultural proxy for the spread of modern humans from the Levantine corridor to Europe, both for the innovations leading to the increased variety of material culture and modern human remains, especially teeth, found in several Aurignacian cultural layers (Benazzi et al. 2015). Even if in southwestern France the Protoaurignacian is always stratigraphically placed below the Early Aurignacian, new evidence from Central Europe indicates a chronological overlapping between the two assumed consecutive stages (Nigst et al. 2014). From a techno-typological point of view the Protoaurignacian is a blade-bladelet dominated industry. Both products are often described to be obtained from the same cores, through a continual reduction sequence (Bon 2002). Among tools, retouched bladelets are the most attested type, followed by end-scrapers, burins and retouched blades. The Early Aurignacian is instead known for the use of two distinct core reduction sequences that result in the production of blades and bladelets. This difference, proposed in order to offer a more appropriate separation between the two techno-complexes, has blurred the variability of methods and technical expedients that were available to those human groups. In this poster we will present the first result of an accurate analysis of the lithic industry found in the Protoaurignacian layers of a key site for the understanding of the earliest Aurignacian: Fumane cave. In layers A2-A1 dwelling structures, lithic assemblages, bone and antler tools, painted stones, and ornamental objects mark the arrival of the first Aurignacians after 41.2 – 40.4 ky cal BP (Higham et al. 2009). The present study considers several thousands of blanks, by-products, retouched tools and cores: this latter category is composed of around 200 artifacts. To describe the material, a combination of two main methods is used: attribute analysis and reduction sequence approach. Cores received special attention in the first part of our research project. Each core was described individually to reconstruct the last steps (position, chronology and direction) of the reduction sequence prior to discard, following Roussel et al. (2016). Preliminary observations were then tested on the material using the body of data obtained through the attribute analysis. Protoaurignacian lithic production at Fumane cave is specialized to the manufacture of retouched bladelets and retouched points (around 80% of the retouched tools). Cores appear always highly exhausted and the last scars show that the main target of the blank production are convergent and slightly curved bladelets. The almost absence of veritable blade cores (only 3 specimens), the dimension of the complete blades and the original dimension of raw material nodules, suggest that the production of blade and bladelets are in most cases integrated, but not exclusively successive, as argued by F. Bon (2002). In most cases long and large blades come from the first stage of core structure preparation (semi-cortical blades, lateral blades and overshot blades). After this stage, small blades and big bladelets were produced in the same reduction phase, during an alternate process. Furthermore, an exclusive bladelets production is well attested. Many of those bladelet cores, mainly produced on small blocks and sometimes slabs, have two or more flaking surfaces, used in succession to optimize the production. Their discard is almost always due to the reflection of the last negatives, due to the flattening of the flaking surface.
The ongoing analyses at Fumane cave reveal that the concept of the Protoaurignacian is still not very well stated from a technological point of view and that the vast geographic area covered by this techno-complex could be characterized by a greater variability, which in our opinion has been minimized to easily track the spread of modern humans across Western Eurasia at the threshold of the Upper Paleolithic
Breaking through the aquitaine frame: A re-evaluation on the significance of regional variants during the Aurignacian as seen from a key record in southern Europe
No full textThe cultural dynamics that led to the appearance of the Aurignacian have intrigued archaeologists since the start of Paleolithic research. However, cultural reconstructions have often focused on a restricted region of Europe, namely the northern Aquitaine Basin. The Mediterranean Basin, though, is also a region worthy of consideration when testing if the Protoaurignacian was followed by the Early Aurignacian adaptive system. Fumane Cave is a pivotal site for tackling this issue because it contains evidence of repeated human occupations during the time span of the European Aurignacian. Here we investigate the diachronic variability of the lithic assemblages from five cultural units at Fumane Cave using a combination of reduction sequence and attribute analyses. This paper also reassesses the presence and stratigraphic reliability of the organic artifacts recovered at Fumane Cave. Our results show that the features of the Protoaurignacian techno-typology are present throughout the stratigraphic sequence, and by extension, to the onset of Heinrich Event 4. Additionally, the appearance of split-based points in the youngest phase is evidence of extensive networks that allowed this technological innovation to spread across different Aurignacian regions
The contribution of integrated 3D model analysis to Protoaurignacian stone tool design
No full textProtoaurignacian foragers relied heavily on the production and use of bladelets. Techno-typological studies of these implements have provided insights into crucial aspects of cultural variability. However, new technologies have seldom been used to quantify patterns of stone tool design. Taking advantage of a new scanning protocol and open-source software, we conduct the first 3D analysis of a Protoaurignacian assemblage, focusing on the selection and modification of blades and bladelets. We study a large dataset of complete blanks and retouched tools from the early Protoaurignacian assemblage at Fumane Cave in northeastern Italy. Our main goal is to validate and refine previous techno-typological considerations employing a 3D geometric morphometrics approach complemented by 2D analysis of cross-section outlines and computation of retouch angle. The encouraging results show the merits of the proposed integrated approach and confirm that bladelets were the main focus of stone knapping at the site. Among modified bladelets, various retouching techniques were applied to achieve specific shape objectives. We suggest that the variability observed among retouched bladelets relates to the design of multi-part artifacts that need to be further explored via renewed experimental and functional studies
Scraping hide in the early Upper Paleolithic: insights into the life and function of the Protoaurignacian endscrapers at Fumane cave
No full textEndscrapers are specialized tools that are usually recovered in great quantities in every Upper Paleolithic site in Europe. Although they make their first ephemeral appearance in the Middle – late Middle Paleolithic transitional technocomplexes, endscrapers commonly appear in tool-kits from initial and early Upper Paleolithic traditions onwards. Nevertheless, endscrapers and, in general, domestic tools have attracted relatively little attention in debates revolving around the significance of technological change, tool-function and tool-specialization after the end of the Middle Paleolithic. With the aim to overcome this paucity of information, here, we present the results of a techno-functional study performed on the large endscraper assemblage recovered from the early and late Protoaurignacian layers at Fumane Cave in northeastern Italy. We analyzed these artefacts using technological, morpho-metrical, typological and functional approaches. Despite the large morphological variability, use-wear traces reveal functional consistency and high levels of specialization for these tools. Almost all the use-wear traces we recorded developed from hide working with transverse motion. Moreover, we find no evidence that endscrapers were involved in the production of bone and antler tools during the late Protoaurignacian. Macroscopic and microscopic wear on the lateral edges of tools point to a considerable number of hafted endscrapers, which implies systematic time investment and planning depth. Comparison with the few endscrapers from transitional industries that have been analyzed highlights marked differences in the production, morphology and use of these tools and reinforces our view of the Aurignacian as a complex not directly related with preceding European traditions
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
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