Strong two-photon-induced fluorescence from a highly soluble polythiophene

Two-photon-induced fluorescence from a soluble polythiophene containing urethane side groups has been investigated using femto-second laser pulses at 800 nm. Strong two-photon fluorescence was measured in polymer solution. The quadratic dependence of the fluorescence on the excitation laser intensity confirmed the two-photon process. The measured two-photon absorption cross-section is larger as compared to those of other reported polythiophenes. This polymer can be readily hydrolyzed to yield a water soluble polythiophene which could be useful in biological imaging.     

Effect of side groups on two-photon absorption of soluble polythiophenes

The effect of pendant side groups on two-photon absorption cross-section in a number of soluble fluorescent polythiophenes was investigated. Different side groups lead to different planarity and conformation of the polymer. As the side-group-induced planarity of the polymer chain increases, the two-photon absorption cross-section also increases. The increased delocalization of the π-electrons along the polymer backbone enhances the third-order optical nonlinearity. The aggregation of the polymer chain in solution lowers the quantum efficiency of fluorescence and decreases the two-photon absorption cross-section. This study demonstrates a novel method of enhancing the two-photon absorption cross-section by tuning the pendant side group.     

Electronic Structure of a Semiconducting Imine‐Covalent Organic Framework

Imine COF (covalent organic framework) based on the Schiff base reaction between p‐phenylenediamine (PDA) and benzene‐1,3,5‐tricarboxaldehyde (TCA) was prepared on the HOPG‐air (air=humid N₂) interface and characterized using different probe microscopies. The role of the molar ratio of TCA and PDA has been explored, and smooth domains of imine COF up to a few μm are formed for a high TCA ratio (>2) compared to PDA. It is also observed that the microscopic roughness of imine COF is strongly influenced by the presence of water (in the reaction chamber) during the Schiff base reaction. The electronic property of imine COF obtained by tunneling spectroscopy and dispersion corrected density functional theory (DFT) calculation are comparable and show semiconducting nature with a band gap of ≈1.8 eV. Further, we show that the frontier orbitals are delocalized entirely over the framework of imine COF. The calculated cohesive energy shows that the stability of imine COF is comparable to that of graphene.     

Solving Posynomial Geometric Programming Problems via Generalized Linear Programming

This paper revisits an efficient procedure for solving posynomial geometric programming (GP) problems, which was initially developed by Avriel et al. The procedure, which used the concept of condensation, was embedded within an algorithm for the more general (signomial) GP problem. It is shown here that a computationally equivalent dual-based algorithm may be independently derived based on some more recent work where the GP primal-dual pair was reformulated as a set of inexact linear programs. The constraint structure of the reformulation provides insight into why the algorithm is successful in avoiding all of the computational problems traditionally associated with dual-based algorithms. Test results indicate that the algorithm can be used to successfully solve large-scale geometric programming problems on a desktop computer.     

Valorization of industrial waste lignin via pyrolysis in the presence of additives: Formation,characterization, and application of fuel valued bio-oil and activated char

The annual production of over 50 million tonnes of industrial waste kraft lignin and scant utilization invites environmental concern. To explore the potential of simultaneously produced bio-oil and modified char (Activated char), lignin from industrial effluents was subjected to pyrolytic degradation at 380 °C using various additives, viz., H₃BO₃, ZnCl₂, and KOH yielding encouraging quantities of bio-oils besides substantial quantities of char. Quantitative and qualitative analyses of gaseous products (by GC-TCD) indicated a mixture of CO, CO₂, H₂, and methane, with some variation in volumetric composition suggesting potential for gaseous fuel/syngas. Gaseous products obtained in the presence of H₃BO₃ have the highest methane percentage. The bio-oils obtained in the presence of H₃BO₃, ZnCl₂, KOH, and only pure lignin under otherwise similar conditions were respectively 37%, 21%, 27%, and 11 wt%. In all cases, mainly bio-oils contain phenols, cyclic esters, and carboxylic acids, as indicated by GC-MS analysis. Elemental (C, H, O) Analyses of bio-oils obtained in the presence of (H₃BO₃, ZnCl₂, and KOH) indicated decreasing oxygen content compared to original lignin, suggesting their prima facie potential to lead to fuel additives/supplements. Similarly, the Char obtained in the presence of H₃BO₃, ZnCl₂, KOH, and only pure lignin were respectively, 40%, 53%, 48%, and 33 wt% with a high calorific value. Char obtained from KOH application demonstrated good uptake of Carbofuran (pesticide) from the aqueous solution. Less modified, cost-effective activated char was characterized using FTIR, TG-DTA, XRD, SEM, and BET-BJH, indicating 188.798 m²/g; this explores the role of KOH to form a microporous structure. Pseudo-second-order kinetics explain chemisorption to be dominant in the adsorption process. Thus, pyrolysis at selected temperatures/additives/and further treatments provides a much better way to utilize industrial waste lignin.     

Multicomponent domino process for the synthesis of some novel 5-(arylidene)-3-((1-aryl-1H-1,2,3-triazol-4-yl)methyl)-thiazolidine-2,4-diones using PEG-400 as an efficient reaction medium and their antimicrobial evaluation

A series of novel thiazolidinedione-triazole hybrids were synthesized by one pot reaction between thiazolidine-2.4-dione,substituted aryl aldehydes,piopargyl bromide and substituted aryl azides using piperidine,CuSO_4· 5H_2O and sodium ascorbate as catalysts in PEG-400 as a highly efficient and green media.These thiazolidinedione-triazole hybrids were subjected to in vitro antibacterial activity against four strains namely.Staphylococcus aureus.Bacillus subtilis,Escherichia coli,Pseudomonas aeruginosa and antifungal activity against two fungal strains namely,Aspergillus niger and Aspergillus flavus.     

Surface tension and vapor-liquid phase coexistence of confined square-well fluid

Phase equilibria of a square-well fluid in planar slit pores with varying slit width are investigated by applying the grand-canonical transition-matrix Monte Carlo (GC-TMMC) with the histogram-reweighting method. The wall-fluid interaction strength was varied from repulsive to attractive such that it is greater than the fluid-fluid interaction strength. The nature of the phase coexistence envelope is in agreement with that given in literature. The surface tension of the vapor-liquid interface is calculated via molecular dynamics simulations. GC-TMMC with finite size scaling is also used to calculate the surface tension. The results from molecular dynamics and GC-TMMC methods are in very good mutual agreement. The vapor-liquid surface tension, under confinement, was found to be lower than the bulk surface tension. However, with the increase of the slit width the surface tension increases. For the case of a square-well fluid in an attractive planar slit pore, the vapor-liquid surface tension exhibits a maximum with respect to wall-fluid interaction energy. We also report estimates of critical properties of confined fluids via the rectilinear diameter approach.     

Computations of a laminar backward‐facing step flow at Re=800 with a spectral domain decomposition method

The two‐dimensional laminar incompressible flow over a backward‐facing step is computed using a spectral domain decomposition approach. A minimum number of subdomains (two) is used; high resolution being achieved by increasing the order of the basis Chebyshev polynomial. Results for the case of a Reynolds number of 800 are presented and compared in detail with benchmark computations. Stable accurate steady flow solutions were obtained using substantially fewer nodes than in previously reported simulations. In addition, the problem of outflow boundary conditions was examined on a shortened domain. Because of their more global nature, spectral methods are particularly sensitive to imposed boundary conditions, which may be exploited in examining the effect of artificial (non‐physical) outflow boundary conditions. Two widely used set of conditions were tested: pseudo stress‐free conditions and zero normal gradient conditions. Contrary to previous results using the finite volume approach, the latter is found to yield a qualitatively erroneous yet stable flow‐field. Copyright © 1999 John Wiley & Sons, Ltd.