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The development of an SPH tree-based algorithm to investigate the evolution of self-gravitating Protoplanetary Disks
Full text linkI Dischi Circumstellari costituiscono un campo di studio molto moderno, per diverse ragioni. Prima di tutto, lo studio dell'evoluzione di tali sistemi mira a spiegare la configurazione delle migliaia di sistemi planetari che sono stati osservati fin ora, e può fornire risposte importanti anche sulla formazione del Sistema Solare.
In secondo luogo, gli sviluppi delle tecnologie interferometriche nella banda Infrarossa e Millimetrica hanno fornito un ampia gamma di possibilità di osservare i dischi con una risoluzione angolare molto piccola. I dischi hanno dunque rappresentato un ampio target osservativo che ha stimolato non in maniera indifferente l'applicazione e il miglioramento delle più avanzate tecniche osservative.
Inoltre, l'evoluzione dei dischi è guidata da diversi processi fisici, sia dinamici sia idrodinamici, e dunque essi figurano tragli oggetti di studio più importanti a cui applciare sofisticate tecniche di modellistica numerica.
In particolare, i dischi Protoplanetari sono diventati, dagli ultimi due decenni, un obbiettivo chiave nel campo dei sistemi stellari multipli. La loro evoluzione in ambienti eterogenei ricchi di stelle e gas rappresenta una nuova frontiera del calcolo numerico applicato all’astronomia, perché implica numerosi problemi ancora irrisolti. Le recenti scoperte di dischi in ammassi aperti ha aperto a nuove prospettive nello studio teorico di sistemi planetari extrasolari nel loro stato primordiale gassoso.
Per queste ragioni, l’attività del mio Dottorato ha come scopo l’implementazione di uno strumento di modellistica numerico, capace di affrontare questi e molti altri problemi legati all’interazione tra gas e stelle. In questo documento, il Sottoscritto presenterà un nuovo algoritmo sviluppato per integrare l’evoluzione temporale di sistemi gassosi (con o senza gravità) e la loro interazione con le stelle. Il codice si basa sul ben noto approccio Smoothed Particles Hydrodynamics (SPH), e contiene un metodo numerico per accoppiare il cas con un limitato numero di punti di massa calcolando, con elevata precisione, la loro mutua interazione gravitazionale. Il calcolo dell’autogravità è fatto approssimando la forza mediante il noto Tree-Scheme.
Dopo aver descritto alcuni test basilari sulla stabilità e sulle prestazioni, il Sottoscritto descriverà il problema astrofisico principale studiato durante il lavoro di dottorato: l’evoluzione di dischi protoplanetari perturbati da stelle che effettuano incontri ravvicinati, che cistituisce uno schema approssimato del più complesso caso di interazione di un disco con l’ambiente stellare in cui esso è immerso.Circumstellar Disks represent a very modern object of investigation, for many reasons. First, the investigation on their evolution aims at explaining the configuration of several thousand of planetary systems detected so far and may give important answers even on the formation of Solar System. Secondly, the early development of the interferometric technique to observe in the infrared and mm wave-length, opened a wide range of possibilities to observe disks with very short angular resolution. Thus, Disks constitute a wide target, stimulating the application and the improvement of the most advanced observational techniques. Moreover, disk evolution is driven by several physical processes, both dynamical and hydrodynamical, they are indeed one of the most important objects of application of several sophisticated numerical techniques.
Protoplanetary disks have become, since the last 20 years, a key target in the field of star clusters. Their evolution in heterogeneous environments rich in stars and gas represents a new frontier for the Numerical Astronomy because it carries several issues still not overcome. The recent discoveries of circumstellar disks in open clusters opened to new perspectives to the theoretical investigations of non-isolated exoplanetary systems in their primordial gaseous state.
For such purposes, my PhD activity aimed at building a suitable numerical investigating instrument, able to face this and many other problems related to the interaction between gaseous systems and stars. In this document, I will present a new Algorithm developed to treat the evolution of gaseous systems (both selfgravitating and non-selfgravitating) and their interaction with Stars. The Code is based on the well-known Lagrangian Smoothed Particle Hydrodynamics approach, and contains a numerical technique to couple a gas distribution with a few amounts of point-mass particles, evaluating,
with high precision, their motion. The calculus of self-gravity is accomplished with a tree-scheme approach.
After describing some basic stability and performance tests, I will focus on the main problem investigated during my work: the evolution of protoplanetary disks perturbed by passing-by stars, which constitute an approximated scheme of the more complex disk-stellar environment interaction
A Tree-based SPH Algorithm to investigate the interaction of a young Binary Star and its gaseous disk.
No full textThe scientific target of my PhD activity in Astronomy, Astrophysics and Space Science, consists in studying several kinds of protostellar gaseous disks around young binary systems, to understand the role of the two stars on the dynamical and thermal evolution of gas.
In this context, I will present some preliminary work, consisting in the implementation of a Tree-based 3D Smoothed Particle Hydrodynamics code. This algorithm is designed to treat multi phase systems made of gas and point-mass particles which can represent both stars and planets. The numerical code is suitably implemented to take efficiently into account both gravitational interactions and the internal thermodynamics in a full Lagrangian approach. The code has been parallelized on shared memory architectures. Some preliminary tests and applications on gas distributions around single and binary systems will be shown.
The main motivation to start writing a new algorithm is to provide a suitable and flexible tool to study a wide ensemble of gas and stars systems, in support of the several topics (in Planetology and in self-gravitating systems) of the research groups I am involved with. In this framework, the study of the role of gas in stellar aggregates represents an important part of the research. To perform such investigations, my algorithm will be easily provided with several additional physical effects, and its level of parallelization will be increased to exploit dedicated hardware of multicore platforms, such as the composite CPU+GPU architectures
A new 3D hydrodynamical tree-based code for the investigation of the evolution of circumbinary radiative self-gravitating gaseous disks.
No full textAt present, the study of the evolution of matter around young binary systems is a key issue which can provide important answers on the possibility of forming planets in stable orbits around two stars. In the context of my PhD work in Astronomy, Astrophysics and Space Science, me and my research group aim at studying the conditions for stability of gaseous disks revolving around binary stars, during the earliest phases of planet formation, when no km-sized planetesimal has been constituted yet and the circumbinary matter is still made up of just gas and dust. The stability of such systems, maintained for a sufficiently large time-scale, will be a crucial condition for matter condensation and for the following planet constitution.
For this purpose, we intend to perform several 3D high resolution simulations by implementing a Smoothed Particle Hydrodynamics tree-based code, suitably designed to take efficiently into account both the selfgravity of the system and the influence of the stellar radiation.
Previously, few works focused their attention to this problem and, to overcome several issues due to computational efforts, some approximations have been used. Despite important constraints for the regions of stability have been obtained, no characterization in high details on the structure of the disk nor clear informations about its symmetry have been given.
By contrast, our code will be realized to take into account several physical processes, relevant for disk stability, exploiting some suitable numerical techniques previously developed by several authors. In particular, self-gravity and stellar radiation absorption, which in many cases have been considered in a simplified theoretical scheme, are thought to play a crucial role. Our algorithm is designed to be flexible, due to its lagrangian structure, and efficient, since it will run in multi-node architectures.
Such poster shows a preliminary part of our work which consists in the realization of a serial version of the code, able to simulate the hydrodynamical evolution of a gas system which interacts gravitationally with two stars (represented by point mass objects)
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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