1,721,135 research outputs found
Exploring the Electronic Structure of an Organic Semiconductor Based on a Compactly Fused Electron Donor-Acceptor Molecule
No full textA Mott-type semiconductor based on a compactly fused and partially oxidized electron donor-acceptor (D-A) molecule was recently prepared and identified to exhibit a large room-temperature conductivity of 2 S cm-1. In a marked contrast to the organic conductors characterized by relatively well decoupled and segregated uniform stacks of D and A moieties, the formally half-oxidized tetrathiafulvalene donors of the actual compound are organized in columnar π stacks only, whereby the coplanar electron-acceptor units, namely benzothiadiazole, are closely annulated along their ridges. Herein, we present a theoretical study that explores the electronic structure of this novel type of organic semiconductor. The highly symmetric-solid state material behaves as a one-dimensional electronic system with strong antiferromagnetic interactions (coupling constant>200 cm-1). The unique shape and local dipole of this redox-active fused electron D-A molecule lays the basis for further investigations of the collective electronic structure, mainly in the function of different counterions embedded in the crystalline lattice
High Pressure Behaviour of the Organic Semiconductor Salt (TTF-BTD)2I3.
Full text link: This study focuses on the effect of structure compression and cooling on the stereoelectronic properties of the planar π-conjugated TTF-BTD (TTF = tetrathiafulvalene; BTD = 2,1,3-benzothiadiazole) molecule, a prototypical example in which an electron-donor moiety is compactly annulated to an electron-acceptor moiety. Its partially oxidised iodine salt (TTF-BTD)2I3 is a crystalline semiconductor featuring segregated columns of TTF+0.5 units stacked via alternating short and long π-π interactions. We studied TTF-BTD at temperatures ranging from 300 K to 90 K and at pressures up to 7.5 GPa, using both X-ray diffraction and Raman spectroscopy to determine the properties of the compressed samples. Periodic DFT calculations and several theoretical tools were employed to characterize the calculated structural modifications and to predict the structural changes up to 60 GPa. The existence of an unprecedented new phase is predicted above 20 GPa, following a covalent bond formation between two neighbouring TTF-BTD units
The Declining and the Thriving Neighborhoods: Urban Regeneration in the Chinese Context of Migration and Economic Transition
No full textIn the past few years, one of the major changes in urban development strategies of the first-tier cities in China is the increasing focus on urban regeneration. To cope with the magnitude of migration and challenges of economic transition, these cities are forced to find new models of urban redevelopment. This has brought up a few challenging questions: How to deal with the ‘old’ typologies of urban neighborhoods, including not only their ‘outdated’ physical environment, but also new lives embedded in the dynamics of emerging social structure and productivity? How to balance interests related to big redevelopment plans of city re-branding and the thriving small businesses bound to the low cost living and working environment in the old neighborhoods? This paper will use Guangzhou as the study case, focusing on two neighborhoods: Kecun, an area with old danwei housing and factories and Lijiao village, an urban village with historical heritages, both of which are accommodating migrants and various types of small businesses. These two neighborhoods are adjacent to the southern section of the new central axis of Guangzhou, which, from the planning perspective, represents the future of the city. As planned, the southern section of the new axis will be extended in the coming years, focusing on an administrative center and multi-functional community for cultural, leisure and public activities. It is bringing large-scale urban regeneration into the adjacent areas, where migrants and small businesses are finding their ways to thrive at the moment. This paper intends to unfold the current socio-economic and spatial transformation happening in the two chosen neighborhoods, especially the role of low-cost living and working environment in enhancing social resilience and economic transition in the local scale. By doing so, the paper will indicate possible ways of creating synergies between the ‘big plans’ and neighborhood-based development. Spatial Planning and Strateg
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
The Shanghai Lilong in the 21st Century: Can Informal Commercial Activity Save this Threatened Urban Space?
No full textLilong were gated, hierarchically organized residential compounds built in Shanghai during the colonial era. Stylistically influenced by the West, they also saw China’s concept of the home (jia) change into something more modern (and Western): the family home, while still a home, could also be seen as a commodity. Once covering 80% of the city, lilong are being replaced by denser urban development. This is bad for the preservation of Shanghai’s unique vernacular architectural heritage, but we may also be losing potentially useful lessons from the past on ways of generating vibrant community life. This paper will examine four recent redevelopments to look at the role of different entrepreneurs, from large, top-down private developers to small, bottom-up individual owners, to determine which, if any, comes closest to best preservingthe spirit of the lilong. Jianyeli is a residential gentrification which not only subverts the typology (by being for the rich) but has killed off any street life; Xintiandi is a hugely successful commercial development, but one in which thereis no provision for residents; Tianzifang is a more bottom-up commercial redevelopment but is too touristic (it does, however, preserve a lively mix of commercial and residential life); finally, there is Jing’an Villa, where earlier this decade there was a temporary but fascinating efflorescence of bottom-up informal commercial activity instigated by the returning descendant of emigrants in one of the best preserved residential lilong in the city. No one redevelopment will point the way to a vibrant future for this threatened typology, but bottom-up informal commercial activity certainly seems a promising way of attempting to preserve it. Combined with lessons from the other redevelopments, we may be able to suggest a better balanced approach to preserving this fascinating and unique urban space for the future.Spatial Planning and Strateg
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
Mycorrhizal type and soil pathogenic fungi mediate tree survival and density dependence in a temperate forest
No full textDispelling 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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