1,721,011 research outputs found
Induced Chirality in Confined Space on Halogen Gold Complexes
No full textThe solubilization of HAuCl4 in toluene within
optically active reverse micelles and lamellar structures formed
by (1R,2S)-Dodecyl(2-hydroxy-1-methyl-2-phenylethyl)-
dimethylammonium bromide (DMEB) has allowed us to
evidence the complex phenomenology accompanying the
confinement of Au salt within these nanostructures. Together
with a chloride/bromide exchange process occurring in the
first coordination sphere of an Au ion, UV−vis and electronic
circular dichroism (ECD) spectra reveal the appearance of an
induced dichroic signal attributable to Au complexes
entrapped in the hydrophilic domain of the DMEB chiral
nanostructures. Interestingly, change of the effective oxidation
state and coordination geometry of the gold ion confined in DMEB nanostructures has been inferred by an analysis of the Au and
Br X-ray Absorption Fine Spectroscopy (X-ray Absorbition Near Edge Spectroscopy and Extended X-ray Absorption Fine
Spectroscopy) signals. Remarkably, bromine, not covalently bonded to the organic part, acts as the vector that transfers the
chirality information on the DMEB to the gold complexes. Structural information on the HAuCl4 solubilized in DMEB reverse
micelles dispersed in toluene, obtained by SAXS, indicate the formation of elongated clusters consisting of Au complexes
stabilized by DMEB, confirming that the chirality transfer occurs in the micellar core of the DMEB and persists in the solid
composites obtained by slow evaporation of the solvent
Nanostructured dimethacrylate-based photopolymerizable systems by modification with diblock copolymers
No full textWe report the full characterization of a photocurable dimethacrylate-based formulation modified with small amounts (1 and 3 wt%) of a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP). The UV curable formulation is a mixture of bisphenol A bis(2-hydroxy-3-methacryloxypropyl)ether (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) and contains phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (Irgacure819) as photoinitiator. We demonstrate that the addition of a small amount of BCP in the uncured formulation is able to induce a phase separation at the nanometer scale. The nanoscale structure formed in the pre-cure stage is retained after the UV curing, so obtaining nanostructured solid cross-linked materials. The studied materials can be used in the manufacturing process of stereolithography and, therefore, in modern 3D printers. The ability to induce and control the formation of nanostructures in the material by adding BCPs in the formulations could open new opportunities to tailor and improve the properties of the 3D printed objects
A Direct Real-Time Observation of Anion Intercalation in Graphite Process and Its Fully Reversibility by SAXS/WAXS Techniques
Full text linkThe process of anion intercalation in graphite and its reversibility plays a crucial role in the next generation energy-storage devices. Herein the reaction mechanism of the aluminum graphite dual ion cell by operando X-ray scattering from small angles to wide angles is investigated. The staging behavior of the graphite intercalation compound (GIC) formation, its phase transitions, and its reversible process are observed for the first time by directly measuring the repeated intercalation distance, along with the microporosity of the cathode graphite. The investigation demonstrates complete reversibility of the electrochemical intercalation process, alongside nano- and micro-structural reorganization of natural graphite induced by intercalation. This work represents a new insight into thermodynamic aspects taking place during intermediate phase transitions in the GIC formation
Controlling Superstructure-Property Relationships via Critical Casimir Assembly of Quantum Dots
Full text linkThe assembly of colloidal quantum dots (QDs) into dense superstructures
holds great promise for the development of novel optoelectronic devices. Several assembly
techniques have been explored; however, achieving direct and precise control over the
interparticle potential that controls the assembly has proven to be challenging. Here, we
exploit the application of critical Casimir forces to drive the growth of QDs into
superstructures. We show that the exquisite temperature-dependence of the critical
Casimir potential offers new opportunities to control the assembly process and
morphology of the resulting QD superstructures. The direct assembly control allows us
to elucidate the relation between structural, optical, and conductive properties of the
critical Casimir-grown QD superstructures. We find that the choice of the temperature
setting the interparticle potential plays a central role in maximizing charge percolation
across QD thin-films. These results open up new directions for controlling the assembly
of nanostructures and their optoelectronic properties
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
Macroscopic Biaxial Order in Multilayer Films of Bent-Core Liquid Crystals Deposited by Combined Langmuir–Blodgett/Langmuir–Schaefer Technique
No full textBent-core liquid crystals, a class of mesogenic compounds with non-linear molecular structures, are well known for their unconventional mesophases, characterized by complex molecular (and supramolecular) ordering and often featuring biaxial and polar properties. In the nematic phase, their unique behavior is manifested in the formation of nano-sized biaxial clusters of layered molecules (cybotactic groups). While this prompted their consideration in the quest for nematic biaxiality, experimental evidence indicates that the cybotactic order is only short-ranged and that the nematic phase is macroscopically uniaxial. By combining atomic force microscopy, neutron reflectivity and wide-angle grazing-incidence X-ray scattering, here, we demonstrate that multilayer films of a bent-core nematic, deposited on silicon by a combined Langmuir–Blodgett and Langmuir–Schaefer approach, exhibit macroscopic in-plane ordering, with the long molecular axis tilted with respect to the sample surface and the short molecular axis (i.e., the apex bisector) aligned along the film compression direction. We thus propose the use of Langmuir films as an effective way to study and control the complex anchoring properties of bent-core liquid crystals
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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