1,720,955 research outputs found
An Efficient Monte Carlo Algorithm for the Fast Equilibration and Atomistic Simulation of Alkanethiol Self-Assembled Monolayers on a Au(111) Substrate
No full textA new Monte Carlo algorithm is presented for the simulation of atomistically detailed alkanethiol self-assembled
monolayers (R−SH) on a Au(111) surface. Built on a set of simpler but also more complex (sometimes
nonphysical) moves, the new algorithm is capable of efficiently driving all alkanethiol molecules to the Au(111) surface, thereby leading to full surface coverage, irrespective of the initial setup of the system. This
circumvents a significant limitation of previous methods in which the simulations typically started from
optimally packed structures on the substrate close to thermal equilibrium. Further, by considering an extended
ensemble of configurations each one of which corresponds to a different value of the sulfur−sulfur repulsive
core potential, σss, and by allowing for configurations to swap between systems characterized by different σss
values, the new algorithm can adequately simulate model R−SH/Au(111) systems for values of σss ranging
from 4.25 Å corresponding to the Hautman−Klein molecular model (J. Chem. Phys. 1989, 91, 4994; 1990,
93, 7483) to 4.97 Å corresponding to the Siepmann−McDonald model (Langmuir 1993, 9, 2351), and
practically any chain length. Detailed results are presented quantifying the efficiency and robustness of the
new method. Representative simulation data for the dependence of the structural and conformational properties
of the formed monolayer on the details of the employed molecular model are reported and discussed; an
investigation of the variation of molecular organization and ordering on the Au(111) substrate for three CH3−(CH2)n−SH/Au(111) systems with n = 9, 15, and 21 is also included
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Atomistic simulation of alkanethiol self-assembled monolayers on different metal sorfaces
No full textSelf-assembled monolayers (SAMs) find numerous applications in a variety of fields: in the production of thin films from organic materials, in optics and electronics, as means for controlling the hydrophobic or hydrophilic behavior of a surface, as coatings for the protection of surfaces from corrosion, in molecular recognition, and more recently even as biosensors. In an effort to understand the mechanisms and interactions controlling chain organization and packing in these systems and how these affect their macroscopic properties, the present thesis has focused on the development of a Monte Carlo (MC) algorithm, built around a set of simpler but also more complex (sometimes nonphysical) moves, for the atomistic simulation of the SAM structures formed by the adsorption of short alkanethiol molecules on a Au(111) surface. The innovation of the MC algorithm is that it is capable of efficiently driving all alkanethiol molecules to the Au(111), thereby leading to full surface coverage, irrespective of the initial setup of the system. This circumvents a significant limitation of previous methods in which the simulation typically starts from optimally packed structures on the substrate that are close to thermal equilibrium. Further, by considering an extended ensemble of configurations each one of which corresponds to a different value of the sulphursulphur repulsive core potential, σss, and by allowing for configurations to swap between different σss values, the new algorithm can adequately simulate model RSH/ Au(111) systems for values of σss ranging from 4.25 A corresponding to the Hautman-Klein molecular model [J. Chem. Phys., 1988; 1989] to 4.97 A corresponding to the Siepmann-McDonald model [Langmuir, 1993]. A thorough investigation of the variation of molecular organization and ordering on the Au(111) substrate with chain length is presented. In a parallel study, the MC method was extended to alkanethiol SAM systems on different metal surfaces. This has allowed us to perform a detailed investigation of the substrate’s effect on the structure and conformation of the above systems through atomistic MC simulations based on a first-principles density functional modeling of the sulphur-metal interaction. Ab initio calculations on a methanethiol molecule adsorbed on gold, silver and platinum surfaces were conducted and the data obtained were used to develop an accurate classical force field which served as an input to the new MC algorithm. Emphasis was given primarily to the study of the effect of the substrate on the structural properties of the simulated R-SH SAM systems, like molecular orientation, molecular conformation, and statistics of gauche defects.Τα αυτό-οργανούμενα μονοστρωματικά συστήματα (self-assembled monolayers, SAMs) παρουσιάζουν μεγάλο τεχνολογικό και βιομηχανικό ενδιαφέρον καθώς προσφέρουν μοναδική ευκαιρία για την κατανόηση των διεπιφανειακών φαινομένων και των διεργασιών που σχετίζονται με αυτά. Ο έλεγχος των ιδιοτήτων διαβροχής και λίπανσης της επιφάνειας, η επιλεκτική ρόφηση διαφόρων ειδών μορίων (π.χ., μεγάλων βιολογικών μορίων) για το σχηματισμό επιπρόσθετου μονοστρώματος προς μία προεπιλεγμένη δομή (π.χ., με συγκεκριμένο μοριακό προσανατολισμό), ο σχεδιασμός βιοαισθητήρων αλλά και άλλα παραδείγματα αποτελούν μερικές μόνο από τις πιο διαδεδομένες εφαρμογές των SAMs. Στην παρούσα εργασία εστιάσαμε στο πιο διαδεδομένο σύστημα SAM, αυτό που δημιουργείται κατά τη ρόφηση μορίων αλκανοθειολών σε επιφάνεια χρυσού (RSH/ Au(111)). Πιο συγκεκριμένα διερευνήσαμε τις δομικές ιδιότητες καθώς και τις ιδιότητες διαμόρφωσης του σχηματιζόμενου μονοστρώματος με τη βοήθεια ενός καινούργιου αλγορίθμου Monte Carlo (MC) που σχεδιάσαμε στο εργαστήριο, βασισμένου σ’ ένα ιδιαίτερα αποδοτικό μίγμα τόσο απλών όσο και πιο σύνθετων (συχνά μη φυσικών) κινήσεων για τη δειγματοληψία απεικονίσεων του συστήματος. Η καινοτομία του αλγόριθμου MC συνίσταται στο ότι, ανεξάρτητα από την αρχική απεικόνιση του συστήματος, έχει την ικανότητα να οδηγεί αποτελεσματικά όλα τα μόρια της αλκανοθειόλης επάνω στο υπόστρωμα του χρυσού με αποτέλεσμα στο τέλος της προσομοίωσης αυτό να χαρακτηρίζεται από 100% επιφανειακή κάλυψη. Κατά τον τρόπο αυτό παρακάμπτεται ένας σημαντικός περιορισμός των προηγούμενων μεθόδων, οι οποίες ουσιαστικά προ-υπέθεταν την αρχική απεικόνιση του συστήματος (στη βάση πειραματικών δεδομένων). Επιπλέον, λαμβάνοντας υπόψη ένα εκτεταμένο σύνολο αντιγράφων του συστήματος καθένα από τα οποία προσομοιώνεται σε μία διαφορετική τιμή της διαμέτρου van der Waals των ατόμων θείου, σss, και επιχειρώντας ανταλλαγές απεικονίσεων μεταξύ συστημάτων με παρακείμενες τιμές σss, ο νέος αλγόριθμος μας επέτρεψε να προσομοιώσουμε αποτελεσματικά πρότυπα συστήματα R-SH/Au(111) για ένα φάσμα τιμών της παραμέτρου σss από 4.25 A που αντιστοιχεί στο μοριακό μοντέλο των Hautman-Klein [J. Chem. Phys., 1988; 1989] έως 4.97 A που αντιστοιχεί στο μοριακό μοντέλο των Siepmann-McDonald [Langmuir, 1993]
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
