1,720,988 research outputs found
On the formation of propylene oxide from propylene in space: gas-phase reactions
Full text linkIn the present article, we have investigated the possibility of forming propylene oxide (PO) from propylene (PE) by bi-molecular reactions. Propylene oxide is the first chiral molecule observed in the interstellar medium, and studying the thermodynamics and kinetics of formation can suggest possible synthetic routes. We have focused our attention on gas-phase reactions, and the presence of an environment is discussed in particular for the possibility of forming it by association reactions. In particular, we have considered radical and ion–molecule reactions. Results show that the main gas-phase route to PO formation is represented by ion–molecule reactions which turn out to be compatible with astrophysical conditions, notably: PE + O + and PE+HO2+. Their final product is not PO, but its ionized variant PO + that can be neutralized by electron capture. The only thermodynamically and kinetically allowed reaction which can directly lead to neutral PO is a collision of PE with a singlet-excited OH + but two competing reactions (leading to PE + and PO +) are thermodynamically favored and thus more plausible in space
Feasibility Study of a Brayton-Based High Temperature Heat Pump for Waste Heat Recovery in Industrial Applications
No full textElectrification of thermal users through heat pumps can be a promising way to enhance the exploitation of increasing renewable electrical capacity, offering significant opportunities for decarbonizing the industrial sector. For this purpose, since commercial vapor compression cycles are not readily viable to displace fossil fuel boilers employed in industrial thermal processes, interest is growing toward high temperature heat pumps (supply temperature > 160 degrees C) and, among them, reverse Brayton cycles. This work proposes an innovative Brayton-based open heat pump cycle applied to a relevant industrial case study, with the aim of upgrading the available waste heat to the required process temperature levels. The on-design performance analysis of the reverse Brayton cycle is conducted using the modular in-house tool WTEMP-EVO. Subsequently, a sensitivity analysis is performed on temperature levels, heat sink, and compressor isentropic efficiency. Finally, an off-design model integrating existing machinery with their characteristic curves is developed to evaluate different system operating conditions, as well as possible solutions to improve system rangeability, establishing the groundwork for the implementation of an experimental prototype. Results show that the analyzed cycle can provide heat at temperatures above 200 degrees C with a coefficient of performance higher than 1.5 and a temperature lift of more than 100 degrees C, demonstrating its potential in the industrial sector
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
A DFT study of the low-lying singlet excited states of the all-trans peridinin in vacuo
No full textThe electronic properties of peridinin (Per) are investigated using density functional theory (DFT) with a time dependent (TD) treatment for transitions from the ground state to the low-lying electronic excited states. The use of a TD-DFT approach was first tested on the simpler beta-carotene molecule in order to see the performances of different functionals. It turns out from the present study that a TD-DFT approach provides a rather good qualitative picture for the electronic properties of this system for which the use of highly correlated ab initio methods with the needed prescriptions, for example, a large enough basis set and/or active space, is still prevented by its large dimension. The vertical transitions of Per obtained in vacuo using TD-DFT are in good agreement with experimental data available in a nonpolar solvent like n-hexane. Vertical energies obtained for the minimum energy structure of Per were also refined, spanning the Per in vacuo conformational space using ab initio molecular dynamics on its ground state hypersurface. These calculations also confirm the reliability of TD-DFT calculations at least on properties available from a dynamical sampling, that is, possible state inversion and partial explanation of bandwidth. Hence, combining these results with TD-DFT calculations, it is possible to better understand some spectroscopic properties of peridinin
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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