Centrifugally spun carbon fibers prepared from aqueous poly(vinylpyrrolidone) solutions as binder-free anodes in lithium-ion batteries

Aqueous solutions of poly(vinylpyrrolidone) (PVP) of various concentrations (20, 25, and 28 wt%) were successfully spun into fibers by centrifugal spinning. The pristine PVP fibers were annealed and carbonized to produce flexible carbon fibers for use as binder-free anodes in lithium-ion batteries. These flexible carbon fibers were prepared by developing a novel three-step heat treatment to reduce the residual stresses in the pristine PVP precursor fibers, and to prevent fiber degradation during carbonization. The thermogravimetric analysis data showed that the annealed fibers yielded a residual mass percentage of 36.0% while the pristine PVP fibers suffered a higher mass loss and only retained 26.5% of original mass above 450 °C (under nitrogen). The electrochemical performance of the carbon-fiber anodes was evaluated by conducting galvanostatic charge/discharge, rate performance, and cycle voltammetry experiments. The 20, 25, and 28 wt% derived binder-free anodes delivered specific charge capacities of 205, 189, and 275 mAh g⁻¹, respectively, after the first cycle at a current density of 100 mA g⁻¹. The results obtained in this work indicate that a feasible pathway towards a large-scale production of carbon-fiber anodes from a 100% aqueous solution can be achieved via centrifugal spinning and subsequent heat treatment.     

Self-doped N-propansulfonic acid polyaniline-polyethylene terephthalate film used as active sensor element for humidity or gas detection

In this work, we report the fabrication of sensors’ element for humidity or gases, prepared by in situ polymerization of aniline N-propansulfonic acid using ammonium persulfate in acidic medium. The polymer is being used in the form of powder or deposited in multiple layers onto the PET film. Various techniques including Fourier Transform infrared (FTIR), ultraviolet-–visible spectroscopy (UV–vis), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the as-prepared sensing materials. The film has been tested for humidity influence, where the significant variations in electrical characteristics were observed, suggesting its usefulness for humidity sensors. Also, for different organic and inorganic gases, a relatively low operating temperature and important sensitivity were observed that indicate its applicability as an active element for general gases sensors. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47743.     

One-step synthesis of graphene supported platinum nanoparticles as electrocatalyst for PEM fuel cells

Here in, we describe an ultrafast, single-step microwave irradiation route (MW) to prepare graphene supported Pt nanoparticles, during which the small Pt nanoparticles are distributed uniformly on a reduced graphene oxide surface. This route provides evident advantages namely low cost, easiness, low time consuming and high yield in comparison to actual chemical methods to develop efficient Pt/rGO catalyst with Pt content close to state-of-the-art commercial composition. The structure and composition of prepared samples have been studied by specific techniques, while the electrocatalytic stability has been studied using ex-situ and in-situ measurements. High performance and electrochemically stable catalyst for PEM fuel cells was developed using the sample with highest loading and good dispersion. The fabricated Pt-rGO-based MEA was investigated for durability under fuel starvation in comparison with commercial Pt/C-based MEA. The electrocatalytic activity was investigated and the electrochemical response revealed the higher stability during accelerated degradation test under fuel starvation in comparison with commercial Pt/C. This study promotes the applicability of described preparation method to noble or transition metal nanoparticles embedded on graphene-based materials.     

Novel Topology in Semiconducting Tetrathiafulvalene Lanthanide Metal-Organic Frameworks

Tetrathiafulvalene tetrabenzoate (TTFTB) and several lanthanide ions self-assemble into metal-organic frameworks (MOFs) that exhibit a novel topology, a (3,3,3,6,6)-coordinated net, which features an unusual ligand coordination mode and stacking motif. The Yb and Lu MOFs are electrically conductive, with pellet conductivity values of 9(7) × 10⁻⁷ and 3(2) × 10⁻⁷ S/cm, respectively. The crystallographically-determined bond lengths indicate partial oxidation of the ligand, with close S ⋅ ⋅ ⋅ S contacts between ligands providing likely charge transport pathways in the material. Magnetometry reveals temperature-independent paramagnetism, consistent with the presence of ligand-based radicals, as well as weak antiferromagnetic coupling between Yb³⁺ centers. These results illustrate the diversity of MOF structures and properties that are accessible with the TTFTB ligand owing to its electroactive nature, propensity for intermolecular interactions, and conformational flexibility.     

Visualization of biological specimens by cryoHVEM

This article describes the operation and the characteristics of cryoHVEM imaging of biological specimens using a top-entry cryostage. The procedure for inserting frozen specimens into the microscope column is also presented. Whole mounts were thus observed under optimal imaging conditions by combining: (i) fixation by fast freezing for structure preservation without exposure to chemicals, (ii) observation in the hydrated (frozen) state or in the dried state without exposure to the atmosphere after the initial fixation by freezing, and (iii) ultrastructural visualization with the key imaging factors of resolution, penetration and beam-induced damage at their best by high-voltage electron microscopy.     

Isotactic polypropylene–vapor grown carbon nanofibers composites: Electrical properties

Nanocomposites have been obtained by dispersing various amounts of vapor grown carbon nanofibers within isotactic polypropylene. Thermal investigations done by differential scanning calorimetry and dynamic mechanical analysis revealed the effect of the vapor grown carbon nanofibers on the melting, crystallization, α, and β relaxations. Direct current electrical features of these nanocomposites have been investigated and related to the thermal features of these nanocomposites. The effect of the loading with carbon nanofibers on the electrical properties of these nanocomposites is discussed within the percolation theory. The percolation threshold was estimated at about 5.5% wt carbon nanofibers. The temperature dependence of the direct current conductivity is analyzed in detail and it is concluded that the electronic hopping is the dominant transport mechanism. A transition from one‐dimensional hopping towards a three‐dimensional hopping was noticed as the concentration of carbon nanofibers was increased from 10% wt to 20% wt carbon nanofiber. The possibility of a differential negative resistivity is suggested. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45297.     

Kekulé structure count in corazulenic fullerenes

Tiling modification in fullerene modeling can be achieved by some map operations. In this respect, sequences of classical operations, or single generalized operations, were used to obtain corannulene-like azulenic patterns. The aromaticity of such cages tessellated by "corazulenic" supra-faces is discussed in terms of several criteria. Particularly, the number of Kekulé valence structures, was considered as a rough measure of the fullerene aromaticity and implicitely of their stability. The covering was given as a pi-electron partition within some Kekulé valence structures. The well-known geometric index of aromaticity HOMA (harmonic oscillator model of aromaticity) enabled the evaluation of local aromaticity of the discussed supra-faces and brought evidence for several dominant Kekulé valence structures.     

Post-growth annealing of type-II GaSb/GaAs quantum dots grown with different V/III ratios

We report the influence of V/III beam-equivalent-pressure ratios and post-growth annealing on the photoluminescence of GaSb quantum dots grown on GaAs(1 0 0) by molecular beam epitaxy. Increasing the V/III beam-equivalent-pressure ratio from 3 to 5 and then to 7 results in decreased photoluminescence intensity and redshifts the photoluminescence wavelength. The post-growth annealing blueshifts the quantum dot photoluminescence emission and decreases the full-width-at-half-maximum of the photoluminescence peak when annealing temperature is increased above 800 °C. The blueshift behavior is found to be independent on the V/III ratios indicating a similar atomic interdiffusion mechanism for all investigated samples regardless of the quantum dot properties. The photoluminescence intensities of the three samples experience an increase after moderate annealing. Whereas the intensity of the sample with the highest V/III ratio further increases, the intensity of the sample with lower V/III ratios decreases again upon higher annealing steps above 900 °C. Furthermore, temperature- and power dependent photoluminescence measurements are performed on as-grown and 870 °C annealed samples with V/III ratios of 3 and 7 in order to study the reduced quantum dot confinement in more detail.     

Linear random vibration by stochastic reduced‐order models

A practical method is developed for calculating statistics of the states of linear dynamic systems with deterministic properties subjected to non‐Gaussian noise and systems with uncertain properties subjected to Gaussian and non‐Gaussian noise. These classes of problems are relevant as most systems have uncertain properties, physical noise is rarely Gaussian, and the classical theory of linear random vibration applies to deterministic systems and can only deliver the first two moments of a system state if the noise is non‐Gaussian. The method (1) is based on approximate representations of all or some of the random elements in the definition of linear random vibration problems by stochastic reduced‐order models (SROMs), that is, simple random elements having a finite number of outcomes of unequal probabilities, (2) can be used to calculate statistics of a system state beyond its first two moments, and (3) establishes bounds on the discrepancy between exact and SROM‐based solutions of linear random vibration problems. The implementation of the method has required to integrate existing and new numerical algorithms. Examples are presented to illustrate the application of the proposed method and assess its accuracy. Copyright © 2009 John Wiley & Sons, Ltd.     

Emotion regulation and decision making under risk and uncertainty.

It is well established that emotion plays a key role in human social and economic decision making. The recent literature on emotion regulation (ER), however, highlights that humans typically make efforts to control emotion experiences. This leaves open the possibility that decision effects previously attributed to acute emotion may be a consequence of acute ER strategies such as cognitive reappraisal and expressive suppression. In Study 1, we manipulated ER of laboratory-induced fear and disgust, and found that the cognitive reappraisal of these negative emotions promotes risky decisions (reduces risk aversion) in the Balloon Analogue Risk Task and is associated with increased performance in the prehunch/hunch period of the Iowa Gambling Task. In Study 2, we found that naturally occurring negative emotions also increase risk aversion in Balloon Analogue Risk Task, but the incidental use of cognitive reappraisal of emotions impedes this effect. We offer evidence that the increased effectiveness of cognitive reappraisal in reducing the experience of emotions underlies its beneficial effects on decision making. (PsycINFO Database Record (c) 2010 APA, all rights reserved)