1,721,025 research outputs found
Thermally Stable Dibenzo[def,mno]chrysene-Based Polymer Solar Cells: Effect of Thermal Annealing on the Morphology and Photovoltaic Performances
No full textThe photovoltaic performances of dibenzo[def,mno]chrysene-based polymer (poly(2,2'-thiophenevinylenthiophene-4,10-[6,12-bis(2-decyltetradecyloxy)-dibenzo[def,mno]chrysene]) ( PTVTC) or poly( 4,10-bithiophene-6,12-bis( 2-decyltetradecyloxy)-dibenzo[def, mno] chrysene) ( PTTC)) solar cells as a function of thermal annealing temperatures from 100 to 180 degrees C are reported. Interestingly, the solar cells with PTTC containing two thiophene units, have superior thermal stability compared to the PTVTC:[6,6]-phenyl-C71-butyric acid methyl ester ( PC71BM) solar cells, in which the PTVTC has two thiophene and vinyl groups. Atomic force microscopy, transmission electron microscopy, and X-ray diffraction demonstrate that morphological stability of PTTC: PC71BM blend films conduces thermally stable photovoltaic performances of PTTC solar cells. Therefore, the PTTC: PC71BM bulk heterojunction solar cells have highly stable efficiency, retaining 97% of its original power conversion efficiency value without PCBM clusters in the blend films even at elevated temperatures. There have been no previous reports on the thermal stability aspect of dibenzo[def, mno] chrysene-based polymer solar cells so far.1133Nsciescopu
Age-related connectivity differences between attention deficit and hyperactivity disorder patients and typically developing subjects: a resting-state functional MRI study
Full text linkAttention deficit and hyperactivity disorder (ADHD) is a disorder characterized by behavioral symptoms including hyperactivity/impulsivity among children, adolescents, and adults. These ADHD related symptoms are influenced by the complex interaction of brain networks which were under explored. We explored age-related brain network differences between ADHD patients and typically developing (TD) subjects using resting state fMRI (rs-fMRI) for three age groups of children, adolescents, and adults. We collected rs-fMRI data from 184 individuals (27 ADHD children and 31 TD children; 32 ADHD adolescents and 32 TD adolescents; and 31 ADHD adults and 31 TD adults). The Brainnetome Atlas was used to define nodes in the network analysis. We compared three age groups of ADHD and TD subjects to identify the distinct regions that could explain age-related brain network differences based on degree centrality, a well-known measure of nodal centrality. The left middle temporal gyrus showed significant interaction effects between disease status (i.e., ADHD or TD) and age (i.e., child, adolescent, or adult) (P < 0.001). Additional regions were identified at a relaxed threshold (P < 0.05). Many of the identified regions (the left inferior frontal gyrus, the left middle temporal gyrus, and the left insular gyrus) were related to cognitive function. The results of our study suggest that aberrant development in cognitive brain regions might be associated with age-related brain network changes in ADHD patients. These findings contribute to better understand how brain function influences the symptoms of ADHD
A novel small molecule based on dithienophosphole oxide for bulk heterojunction solar cells without pre- or post-treatments
No full textA novel small molecule (PDTP-WR) with a dithieno[3,2- b:2��,3��- d ]phosphole oxide (DTP) core unit was designed and synthesized for use in BHJ solar cells. This small molecule had an optical band gap of 1.65?eV, appropriate for a donor material, and HOMO and LUMO energy levels of??5.10, and??3.45?eV, respectively, which provided a broad absorption and superior charge transfer properties. The solar cell devices prepared using PDTP-WR and PC71BM gave a promising power conversion efficiency of 5.04%, a Jsc of 12.98?mA?cm?2, a Voc of 0.79?V, and a fill factor of 49%, without pre- or post-treatments. Morphological and structural studies revealed that PDTP-WR formed a favorable BHJ morphology. An appropriate domain size of less than 20?nm and bi-continuous interpenetrating paths with an ordered structure obtained as a result of strong intermolecular interactions can support the device performances. This is the first reported use of DTP in small molecule donor, and the results of these studies indicated that DTP-based small molecule can be a promising candidate for the photovoltaic applications. ? 2017 Elsevier Ltd113sciescopu
Two-step deep neural network for segmentation of deep white matter hyperintensities in migraineurs
Full text linkBackground and Objective: Patients with migraine show an increased presence of white matter hyperin- tensities (WMHs), especially deep WMHs. Segmentation of small, deep WMHs is a critical issue in man- aging migraine care. Here, we aim to develop a novel approach to segmenting deep WMHs using deep neural networks based on the U-Net. Methods: 148 non-elderly subjects with migraine were recruited for this study. Our model consists of two networks: the first identifies potential deep WMH candidates, and the second reduces the false positives within the candidates. The first network for initial segmentation includes four down-sampling layers and four up-sampling layers to sort the candidates. The second network for false positive reduction uses a smaller field-of-view and depth than the first network to increase utilization of local information. Results: Our proposed model segments deep WMHs with a high true positive rate of 0.88, a low false discovery rate of 0.13, and F 1 score of 0.88 tested with ten-fold cross-validation. Our model was automatic and performed better than existing models based on conventional machine learning. Conclusion: We developed a novel segmentation framework tailored for deep WMHs using U-Net. Our algorithm is open-access to promote future research in quantifying deep WMHs and might contribute to the effective management of WMHs in migraineurs. ©2019 Elsevier B.V. All rights reserved.11Nsciescopu
The importance of the polymer molecular weight and the processing solvent in PBDTTT-C:PCBM bulk heterojunction solar cells: Their effects on the nanostructrural active texture
No full textThis study presents how the polymer molecular weight (M-w) of PBDTTT-C affects the PBDTTT-C:PC71BM nanoscale morphology and device performances. In particular, this work demonstrates that different M-w, values of the PBDTTT-C are optimized for different processing solvents, leading to various morphological characteristics, as thoroughly examined by atomic force microscopy, transmission electron microscopy and X-ray diffraction. Thus, when PBDTTT-C with a relatively low molecular weight is used, an optimal blend texture that supports efficient charge transport to ideally connected crystalline structures can be obtained through a treatment with chloroform as a processing solvent. As a result, significantly enhanced power conversion efficiency (PCE, over 5.5%) is achieved. These findings highlight the important role of the molecular weight with regard to device performance capabilities and may help in the further development of novel, efficient donor polymers with lower bandgaps for photovoltaic applications. (C) 2016 Elsevier Ltd. All rights reserved.This study presents how the polymer molecular weight (M-w) of PBDTTT-C affects the PBDTTT-C:PC71BM nanoscale morphology and device performances. In particular, this work demonstrates that different M-w, values of the PBDTTT-C are optimized for different processing solvents, leading to various morphological characteristics, as thoroughly examined by atomic force microscopy, transmission electron microscopy and X-ray diffraction. Thus, when PBDTTT-C with a relatively low molecular weight is used, an optimal blend texture that supports efficient charge transport to ideally connected crystalline structures can be obtained through a treatment with chloroform as a processing solvent. As a result, significantly enhanced power conversion efficiency (PCE, over 5.5%) is achieved. These findings highlight the important role of the molecular weight with regard to device performance capabilities and may help in the further development of novel, efficient donor polymers with lower bandgaps for photovoltaic applications. (C) 2016 Elsevier Ltd. All rights reserved.12
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
- …
