1,720,996 research outputs found
Design of Polymeric Self-Assembling Materials and Nanocomposites in the Semi-dilute Density Regime: Multiscale Modeling
No full textExploiting Scaling Laws for Designing Polymeric Bottle Brushes: a Theoretical Coarse-Graining for Homopolymeric Branched Polymers
No full textBottle brushes are polymeric macromolecules made of a linear polymeric backbone grafted with
side chains. The choice of the grafting density sg, of the length ns of the grafted side chains
and their chemical nature, fully determines the properties of each macromolecule, such as its
elasticity and its folding behaviour. Typically experimental bottle brushes are systems made of
tens of thousands of monomeric units, rendering a computational approach extremely expensive,
especially in the case of bottle brushes solutions. A proper coarse graining description of these
macromolecules, thus appears essential. We here present a theoretical approach able to develop
a general, transferable and analytical multi-scale coarse graining of homopolymeric bottle brush
polymers under good solvent condition. Starting from scaling theories, each macromolecule is
mapped onto a chain of tethered star polymers, whose effective potential is known from scaling
predictions, computational and experimental validations and can be expressed as a function of
the number of arms f , and on the length na of each arm. Stars are then tethered to one another
and the effective potentials between them is shown to only depend on the key parameters of
the original bottle brush polymer (sg, ns). The generalised form of the effective potential is then
used to reproduce properties of the macromolecules obtained both with scaling theories and with
simulations. The general form of the effective potentials derived in the current study, allows to
describe theoretically and computationally properties of homopolymeric bottle brush polymers for
all grafting densities and all lengths of both backbone and grafted arms, opening the path for a
manifold of applications
Off-equilibrium confined dynamics in a system with level-crossing states
No full textWe study analytically the dynamics of a generalized p-spin model, starting with a thermalized initial condition. The model presents birth and death of states, hence the dynamics (even starting at equilibrium) may go out of equilibrium when the temperature is varied. We give a full description of this constrained out-of-equilibrium behavior and we clarify the connection to the thermodynamics by computing (subdominant) TAP states, constrained to the starting equilibrium configuration.We study analytically the dynamics of a generalized p-spin model, starting with a thermalized initial condition. The model presents birth and death of states, hence the dynamics (even starting at equilibrium) may go out of equilibrium when the temperature is varied. We give a full description of this constrained out-of-equilibrium behavior and we clarify the connection to the thermodynamics by computing (subdominant) TAP states, constrained to the starting equilibrium configuration
Does the Artemidorus papyrus have multiple lives? Seeking for the answer in the inks through a Raman and PCA analysis
No full textArtemidorus papyrus has been the subject of a longstanding dispute around its authenticity. The 2.5 m long document, presents a multiplicity of writings, on both sides. Some historians support the papyrus’ multiple life hypothesis (PMLH): the different writings appearing on the document, would correspond to three time periods (1st BC–1st AD) called the “three lives of the papyrus”.
A possible way to assess whether the document has been written in different eras, is the analysis of the graphic materials employed; a heterogeneous formulation of the inks used throughout the papyrus as a whole, together with a local homogeneity in defined regions, would support PMLH.
To unveil this paradigm, we performed an in-depth investigation of the inks on the papyrus, by collecting their Raman spectra on a statistical relevant number of samples belonging to the different regions of the document.
We found a wide variety of carbon-based inks that appear to be randomly distributed on the entire surface.
Different ordered, disordered, crystalline or amorphous structures might coexist in carbon-based materials, due to the different hybridisations of the carbon.
All of the different structures appear as peaks, shoulders or sub peaks that are convoluted in the global spectrum, thus rendering the attribution of Raman peaks as an extremely complex task.
In order to support and guide our analysis, we therefore implemented a Principal Component Analysis (PCA) aimed at performing a two-step comparison between the Artemidorus inks Raman spectra and an ample reference spectral library on carbon-based materials that we built specifically for this study.
A first PCA screening was used to restrict the analysis for similarity between the experimental spectra and the library of standards to a subset of compounds. It was indeed possible to define a cluster in the Principal Component subspace that contained only a few standards and the whole set of Artemidorus spectra. It is interesting to notice that, among the possibilities in the reference library, our analysis also found two pigments manufactured with modern industrial methods: Carbon black (after 1870) and lampblack (after 1740, modified in 19th c.). A second PCA, performed on the subset of the standard spectra individuated, allowed to highlight the regions of the Raman spectra where the Artemidorus data depict significant differences with respect to their reference standards, thus allowing for a guided deconvolution of the Raman peaks.
This study demonstrates that it is not possible to define neat regions on the papyrus that would be identifiable through the usage of different groups of inks, as the same subset of inks is distributed on all of the document. It is therefore impossible to recognise areas of the papyrus where the local usage of specific and region-dependent graphic materials would lead to chronologically distinguishable writings and drawings. This allows us to confute the “three lives hypothesis”
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
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