Derivations and spectral triples on quantum domains II: Quantum annulus

Science China Mathematics - Continuing our study of spectral triples on quantum domains, we look at unbounded invariant and covariant derivations in the quantum annulus. In particular, we...     

A sol–gel polymerization method for creating nanoporous polyimide silsesquioxane nanostructures as soft dielectric materials

A sol–gel polymerization method was developed to make polyimide (PI) silsesquioxane (SSQ) nanoparticles as functional, soft dielectric materials. The surface functionalization of the polymer chain backbone and chain ends of poly(trimellitic anhydride chloride‐co‐4,4′‐methylenedianiline), PMR‐15 resin, with para‐(chloromethyl)‐phenylethyltrimethoxy silane yielded a novel sol–gel reactive sites functionalized PMR‐silane precursor. Upon base‐catalyzed hydrolysis and condensation of the PMR‐silane precursor, spherical, raspberry‐like PMR‐SSQ nanoparticles were obtained in considerably good yield. Controlling the particle size distribution was attempted upon adjusting the molar ratio between the silane precursor and the base, as well as in the presence of a catalytic amount of silica sols. Particle composition, thermal stability, and morphology were confirmed from Fourier transform infrared, thermogravimetric analysis, and scanning electron microscopy analyses. Nanoparticles, visualized under transmission electron microscopy exhibit a nanoporous structure. The Brunauer–Emmett–Teller analysis confirmed that the average pore dimension is ranged from 2 to 5 nm. The dielectric constant of PMR‐SSQ nanoparticles was as low as 1.95, compared to dielectric constants of 3.05 and 3.13 for PMR‐15 and PMR‐silane, respectively. Thus, the base‐catalyzed sol–gel polymerization of alkoxysilylated PI offers a novel synthetic path to make functional nanoporous PI nanostructures that possess ultralow dielectric constants. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 57, 562–571.     

Preparation and characterization of 1-ethyl-3-methylimidazolium chloride–based gel polymer electrolyte in electrochemical double-layer capacitors

Journal of Solid State Electrochemistry - Electrochemical double-layer capacitors (EDLCs) have recently received an enormous attraction due to their ability to produce higher power density without...     

Single-molecule studies of a model fluorenone.

Single-molecule fluorescence measurements of 2,7-bis(3,4,5-trimethoxyphenylethenyl)fluorenone (OFOPV) reveal narrow emission spectra concentrated around 540 nm, with weak emission at longer wavelengths. The wide scattering of emission-maximum wavelengths is attributed to varying molecular environments, with dimers or higher-order aggregates contributing to the low-energy emission. This spectral distribution indicates that emission from monomers of this model fluorenone is mostly green, which is consistent with contaminant emission (g-bands) often observed in fluorene- and polyfluorene-based organic light emitting diode (OLED) devices. A histogram of center wavelengths from 118 single-molecule spectra shows good agreement with the green emission previously observed in thermally stressed 2,7-bis(3,4,5-trimethoxyphenylethenyl)-9,9-diethylfluorene (OFPV). Whereas bulk OFPV exhibits blue fluorescence at about 480 nm, OFOPV bulk thin film measurements reveal red luminescence shifted to 630 nm. This unexpected peak position for bulk OFOPV shifts to higher energies (ca. 540 nm) upon dilution in a solid-state matrix, suggesting that the bulk red emission finds its origins in interactions between fluorenone molecules. Explanations for this red emission include aggregate or excimer formation or intermolecular energy transfer between fluorenone molecules.     

A very fast algorithm for matrix factorization

We present a very fast algorithm for general matrix factorization of a data matrix for use in the statistical analysis of high-dimensional data via latent factors. Such data are prevalent across many application areas and generate an ever-increasing demand for methods of dimension reduction in order to undertake the statistical analysis of interest. Our algorithm uses a gradient-based approach which can be used with an arbitrary loss function provided the latter is differentiable. The speed and effectiveness of our algorithm for dimension reduction is demonstrated in the context of supervised classification of some real high-dimensional data sets from the bioinformatics literature.     

A novel donor–donor polymeric dyad of Poly(3‐hexylthiophene‐block‐oligo(anthracene‐9,10‐diyl): Synthesis,solid‐state packing,and electronic properties

A new polymeric dyad of oligo‐anthracene‐block‐poly(3‐hexylthiophene) (Oligo‐ANT‐b‐P3HT) has been synthesized as a donor–donor dyad building block for organic photovoltaics. The polymer dyad and oligomer of anthracene‐9,10‐diyl (Oligo‐ANT) are prepared by Grignard Metathesis. The higher order of crystallinity and molecular chains ordering at solid phase reveal the intrinsic optical and electrical properties of polymeric dyad resulting in relatively higher light harvesting ability compared to the oligo(anthracene‐9,10‐diyl). The UV‐visible spectrum of (Oligo‐ANT‐b‐P3HT) in solution shows broad absorption with two sets of absorption from both anthracene and thiophene core units, covering a wide range of the visible spectrum. The test devices of the blends of polymeric dyad with fullerene C₆₁ (PCBM) show improved photovoltaic performance with a power conversion efficiency of 3.26% upon subjecting to pre‐fabrication thermal treatments. With optimized morphology of the interpenetrating network and the shorter fluorescence lifetime of the annealed dyad/PCBM blends, the effective charge transfer from the donor dyad to PCBM has evidenced. Thus, these studies will allow further synthetic advances to make potential high crystalline polymeric dyads with significantly improved light harvesting capability. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3032–3045     

Chemical investigation of metabolites produced by an endophytic fungi Phialemonium curvatum from the leaves of Passiflora edulis

Phialemonium curvatum, an endophytic fungus isolated from the leaves of Passiflora edulis was cultured in potato dextrose broth (PDB) media and chromatographic separation of the EtOAc extract of the broth and mycelium led to the isolation of 4-hydroxybenzoic acid (1), 3-indole acetic acid (2), solaniol (3), uracil (4), uridine (5) and glycerol (6). Compound 2 showed a weak antifungal activity against Cladosporium cladosporioides. This is the first report of the isolation of the endophytic fungus P. curvatum from P. edulis and complete ¹³CNMR assignments of 3.     

Photoredox catalysis on unactivated substrates with strongly reducing iridium photosensitizers

Photoredox catalysis has emerged as a powerful strategy in synthetic organic chemistry, but substrates that are difficult to reduce either require complex reaction conditions or are not amenable at all to photoredox transformations. In this work, we show that strong bis-cyclometalated iridium photoreductants with electron-rich β-diketiminate (NacNac) ancillary ligands enable high-yielding photoredox transformations of challenging substrates with very simple reaction conditions that require only a single sacrificial reagent. Using blue or green visible-light activation we demonstrate a variety of reactions, which include hydrodehalogenation, cyclization, intramolecular radical addition, and prenylation via radical-mediated pathways, with optimized conditions that only require the photocatalyst and a sacrificial reductant/hydrogen atom donor. Many of these reactions involve organobromide and organochloride substrates which in the past have had limited utility in photoredox catalysis. This work paves the way for the continued expansion of the substrate scope in photoredox catalysis.

Strong bis-cyclometalated iridium photoreductants, in combination with a single sacrificial reductant, enable visible-light-promoted reductive activation of a variety of challenging substrates under simple and general reaction conditions.     

XRF to support food traceability studies: Classification of Sri Lankan tea based on their region of origin

Food fraud is a concern for the producers of high‐quality food products as it causes brand damage and loss of profit. Tea (Camellia sinensis L.) is one of the major agricultural products of Sri Lanka and accounts for more than 300 million of kilograms per year, roughly 2% of the national GDP. Trace metals and stable isotope ratios in tea samples originating from various regions in Sri Lanka were determined by using X‐ray fluorescence analysis and isotope‐ratio mass spectrometry to explore the possibility of classifying the tea according to its origin. In total, 13 elements (Mg, P, S, Cl, K, Ca, Mn, Fe, Cu, Zn, Br, Rb and Sr) were determined in 58 tea samples originating from four production districts in Sri Lanka (Hantana, Thalawakelle, Passara and Ratnapura). Two multivariate analysis techniques, namely principal component analysis and canonical discriminant analysis, were applied to explore the differences in elemental contents among the tea produced in these regions and to find a method for compositional classification. This study, although limited by the number of samples available, clearly shows that the differentiation and classification of tea samples according to the four regions of origin is possible by using the elemental contents and applying canonical discriminant analysis. Copyright © 2017 John Wiley & Sons, Ltd.     

Polyethylene oxide and ionic liquid-based solid polymer electrolyte for rechargeable magnesium batteries

Solid polymer electrolytes (SPEs) based on polyethylene oxide (PEO) complexed with magnesium triflate Mg(Tf)₂ or Mg(CF₃SO₃)₂) and incorporating the ionic liquid (IL) (1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₄TFSI)) were prepared by solution cast technique. The electrolyte was optimized and characterized using electrical conductivity, cationic transport number measurements, and cyclic voltammetry. The highest conductivity of the PEO/Mg(Tf)₂, 15:1 (molar ratio), electrolyte at room temperature was 1.19 × 10⁻⁴ S cm⁻¹ and this was increased to 3.66 × 10⁻⁴ S cm⁻¹ with the addition of 10 wt.% ionic liquid. A significant increase in the Mg²⁺ ion transport number was observed with increasing content of the ionic liquid in the PEO-Mg(Tf)₂ electrolyte. The maximum Mg²⁺ ion transport number obtained was 0.40 at the optimized electrolyte composition. A battery of the configuration Mg/ and [(PEO)₁₅:Mg(Tf)₂+10%IL]/TiO₂-C was assembled and characterized. Preliminary studies showed that the discharge capacity of the battery was 45 mA h g⁻¹.