1,720,959 research outputs found
Hydrophobicity of molecular-scale textured surfaces: The case of zeolitic imidazolate frameworks, an atomistic perspective
No full textHydrophobicity has proven fundamental in an inexhaustible amount of everyday applications. Material hydrophobicity is determined by chemical composition and geometrical characteristics of its macroscopic surface. Surface roughness or texturing enhances intrinsic hydrophilic or hydrophobic characteristics of a material. Here we consider crystalline surfaces presenting molecular-scale texturing typical of crystalline porous materials, e.g., metal-organic frameworks. In particular, we investigate one such material with remarkable hydrophobic qualities, ZIF-8. We show that ZIF-8 hydrophobicity is driven not only by its chemical composition but also its sub-nanoscale surface corrugations, a physical enhancement rare amongst hydrophobes. Studying ZIF-8’s hydrophobic properties is challenging as experimentally it is difficult to distinguish between the materials’ and the macroscopic corrugations’ contributions to the hydrophobicity. The computational contact angle determination is also difficult as the standard “geometric” technique of liquid nanodroplet deposition is prone to many artifacts. Here, we characterise ZIF-8 hydrophobicity via: (i) the “geometric” approach and (ii) the “energetic” method, utilising the Young-Dupré formula and computationally determining the liquid-solid adhesion energy. Both approaches reveal nanoscale Wenzel-like bathing of the corrugated surface. Moreover, we illustrate the importance of surface linker termination in ZIF-8 hydrophobicity, which reduces when varied from sp3 N to sp2 N termination. We also consider halogenated analogues of the methyl-imidazole linker, which promote the transition from nanoWenzel-like to nanoCassie-Baxter-like states, further enhancing surface hydrophobicity. Present results reveal the complex interface physics and chemistry between water and complex porous, molecular crystalline surfaces, providing a hint to tune their hydrophobicity
Triboelectrification During Water Intrusion–Extrusion into‐from Hydrophobic Nanopores
No full textTriboelectrification is of great importance for many classical (petroleum, pharmaceutical, polymers) and emerging (generators, sensors) technologies. For energy generation, the contact area between the materials experiencing tribocharging is a key parameter: in addition to the nature of the materials, tribocharging scales with contact area. In this work, an approach is proposed to maximize tribocharging contact area by exploring the cycle of water intrusion–extrusion into–from hydrophobic nanopores with surface area orders of magnitude higher compared to flat or even nanotextured surfaces. Here this study reports the first experimental evidence of electrical energy generation upon water intrusion-extrusion cycle under bias voltage-free conditions. Combining these experiments with hierarchical molecular dynamic simulations/ab initio calculations, a microscopic mechanism of triboelectrification is hypothesized for water and grafted silica. The proposed approach provides a methodological alternative to studying solid–liquid contact electrification and an alternative root for a noticeable increase of specific contact area for solid–liquid triboelectric nanogenerators
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
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
The Accuracy of Electron Density from Theory : Calculating Electric Field Gradients and X-ray Scattering for Molecules and Solutions
Get PDFPh. D. Thesis.Electron density is the principle determinant of the characteristic properties
of molecules, their structure and dynamics. For this reason it is vital
to ascertain accurate densities. One method of predicting electron densities
is density functional theory (DFT). It is derived from the Hohenburg-Kohn
theorem which states that an exact ground-state energy should yield an exact
electron density and vice versa. In reality the exact solution is not fully
known as exchange and correlation have to be estimated. Were it known,
accurate densities and energies could be calculated at a fraction of ab initio
computational cost. However, it is noted that functional methods have deviated
from the path to the exact functional due to energetic overfitting. This
study used the electric field gradient (EFG) as an electron-density probe to
facilitate comparison both to ab initio calculation (CCSD(T)) and microwave
spectroscopy for simple transition metal complexes and halogenated aromatic
compounds. EFGs improved with increased Hartree-Fock (HF) exchange
fraction encountered for higher rungs of Jacob’s Ladder due to selfinteraction
error (SIE) reduction. SIE cancellation was uneven between transition
metals, halogens and aromatic rings, causing functional-dependent
electronegativity. Electron density can also be inferred from X-ray scattering.
X-ray free-electron lasers (XFELs) are used to probe molecular structure
and dynamics on ultrafast time scales. Solutions contains additional
scattering signals other than the desired solute from the solvent and solutesolvent.
The solvent term can be extracted experimentally or via molecular
dynamics (MD) trajectories. Theory is also the only method of predicting the
solute-solvent term independently. The solvent force-field parameters can
be derived from experiment or theoretically from DFT calculation. The impact
of the chosen force field on the the predicted scattering profiles was
evaluated herein, Quantum Bespoke Kit (QUBE) and all-atom Optimised
Potentials for Liquid Simulations (OPLS-AA) force-fields were used to assess
theoretically- and experimentally-derived parameters respectively for
common solvents for the same test solute (I2). Force-field dependence is elucidated
for both terms due to differences in non-bonded parameters.There
also remains further investigation to better approximate experimental solvent
terms. Solute-solvent scattering occurs on comparable scales to the solute
scattering. XFELs have also been applied recently to improve understanding
metal-to-ligand charge transfer (MLCT) in transition metal complexes
and the influence of polar solvents in their structures. QUBE was
used to investigate the ground and excited states of [Cu(phen)2]+ and compared
to recent classical MD and quantum-mechanical/molecular mechanical
(QM/MM) simulations. It performed particularly well in regards to identifying
Cu-N bond asymmetry and solvent influence in the ligand-ligand
dihedral in the triplet state which were not identified in previous theoretical
investigation but in agreement with recent experimental understanding.
This improvement was attributed to its use of high-rung DFT in parameterisation
(wB97X-D). Overall this investigation evaluate thoroughly the current
state of theory in reproducing accurate electron densities, highlighting the
importance of reducing DFT SIE to improve density accuracy, which in turn
impacts force-field parameter quality, indicating that DFT improvement impacts
all branches of theoretical chemistry
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
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