Enhancement of single-molecule fluorescence using a gold nanoparticle as an optical nanoantenna

We investigate the coupling of a single molecule to a single spherical gold nanoparticle acting as a nanoantenna. Using scanning probe technology, we position the particle in front of the molecule with nanometer accuracy and measure a strong enhancement of more than 20 times in the fluorescence intensity simultaneous to a 20-fold shortening of the excited state lifetime. Comparisons with three-dimensional calculations guide us to decipher the contributions of the excitation enhancement, spontaneous emission modification, and quenching. Furthermore, we provide direct evidence for the role of the particle plasmon resonance in the molecular excitation and emission processes.     

Nonlinear Triple Product $$A^{*}B + B^{*}A$$ for Derivations on $$\ast$$ -Algebras

Mathematical Notes - Let $$\mathcal{A}$$ be a prime $$\ast$$ -algebra. In this paper, assuming that $$\Phi:\mathcal{A}\to\mathcal{A}$$ satisfies $$\Phi(A\diamond B \diamond C)=\Phi(A)\diamond B...     

Simulation of styrene free radical polymerization over bi-functional initiators using Monte Carlo simulation method and comparison with mono-functional initiators

In the present study, based on a complete mechanism, a Monte Carlo simulation method is employed to investigate the kinetics of styrene free radical polymerization over bi-functional initiators in a bulk medium. The effects of the concentration of initiator and the monomer, of the temperature on monomer conversion, average molecular weights, polydispersity index, and molecular weight distribution are inspected and compared with mono-functional initiators. According to the simulation results, an increase in either the concentration of initiator or the temperature leads to the rise of the monomer conversion and to the reduction of the average molecular weights, while the increase of the monomer concentration results in the rise of both monomer conversion and molecular weights, which is in accord with predictions of the theory of free-radical polymerization. In addition, application of bi-functional initiators increases both monomer conversion and average molecular weight and results in narrower chain length distributions.     

Electrical switching studies of lead-doped germanium telluride glasses

Samples of bulk Ge₂₀Te_80-xPb_x(2x8) glasses have been prepared by melt quenching and their electrical switching behavior has been investigated as a function of lead content and sample thickness. The samples are found to exhibit a threshold type of switching. The switching voltages are found to decrease with increase in lead content and they show an anomaly at the composition x=5 and a minimum at the composition x=7.5 respectively. The samples are found to withstand about 28 switching cycles, before latching permanently to the ON state. PACS 61.43.Dq; 61.43.Fs; 72.20.Ht; 72.80.Ng; 73.61.Jc; 84.32.Dd; 85.30.Fg     

A catalytic multicomponent protocol to dihydropyridine-3-carboxylate from terminal alkynes,isocyanates, and malonates

Monatshefte für Chemie - Chemical Monthly - A domino catalytic reaction between terminal alkynes, isocyanates, and malonates has been developed. Copper acetylides attack on isocyanates to form...     

Technological and economical analysis of flare recovery methods,and comparison of different steam and power generation systems

Journal of Thermal Analysis and Calorimetry - One of the most important environmental issues in the oil, gas, and petrochemical industries is the appropriate disposal of waste hydrocarbon gases in...     

Pore-Level Observation of Free Gravity Drainage of Oil in Fractured Porous Media

This work presents results from two sets of experiments conducted to study, in pore level, the role of fracture aperture and tilt angle on the stability of liquid bridges and the shape of a front during free gravity drainage process. Glass micromodels of two different aperture sizes were used to monitor the mechanism of gravity drainage of air?Ccrude oil system, rotating around a bottom corner to create different tilting angles. Oil content within the matrix blocks was determined as a function of time using a series of images obtained during the experiments, from which net drainage rate from the upper and lower matrix blocks is calculated. Liquid bridges are more frequent but less stable at early time of drainage. The liquid bridges, which have widths as thin as 50 ??m, can resist instability to maintain continuity. Liquid bridges formed in stacks with higher tilt angles are more stable, enhancing oil drainage from the upper matrix block and causing higher recoveries. Quantitative analysis of the results shows that a wider fracture aperture increases the oil production rate, but reduces the ultimate recovery. Furthermore, stacks with higher tilt angles present larger ultimate recoveries and smaller production rates. The front geometry in the lower block deviates from linearity due to formation of liquid bridges in the middle fracture. The results of this work can be helpful to better understand the interaction between fractures and matrix blocks.     

Matrix‐grafted multiwalled carbon nanotubes/poly(methyl methacrylate) nanocomposites synthesized by in situ RAFT polymerization: A kinetic study

A new approach was developed to functionalize multiwalled carbon nanotubes (MWCNTs) with a polymerizable methyl methacrylate (MMA) groups, and the structure of functionalized MWCNTs were characterized by FTIR, Raman, XPS, and TEM. Using the strategy of “grafting through,” poly(methyl methacrylate) (PMMA) chains were grafted onto the surface of MWCNTs during the in situ synthesis of MWCNT/PMMA nanocomposites over reversible addition‐fragmentation chain transfer (RAFT) polymerization. Kinetics of RAFT‐mediated polymerization of MMA in the presence of MMA‐grafted MWCNTs was studied by using gas chromatography and gel permeation chromatography. To further study, attached polymers were detached and their molecular characteristics were compared to freely formed chains. Results of kinetic studies showed that the utilized commercial chain transfer agent strictly reduced the rate of polymerization as well as relatively controlled molecular weights and narrow molecular weight distributions of free chains. MWCNTs showed a radical activity, retarding the polymerization and reducing the rate of reaction. The effect of MWCNTs concentrations on molecular weights and polydispersity indexes (PDI) was different at the surface and in the bulk. The molecular weights of free chains increased, and the PDI was decreased with increasing MWCNTs. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 555–569, 2012     

Palladium(II) Immobilized Onto the Glucose Functionalized Magnetic Nanoparticle as a New and Efficient Catalyst for the One‐pot Synthesis of Benzoxazoles

Palladium(II) have been immobilized into the nano magnetic Fe₃O₄ which was functionalized with glucose in order to achieve a one‐pot synthesis of 2‐substituted benzoxazole derivatives with high yields in the diverse range of organic solvents. The nano catalyst is highly dispersive in polar solvents and can be easily recovered and reused for 6 runs without significant loss of its activity. Finally, the catalyst was fully characterized by FT‐IR, TGA, CHN, SEM, EDX and atomic absorption spectroscopy.     

Vitamin B12 supported on graphene oxide: As a bio‐based catalyst for selective aerobic oxidation of alcohols

The environmental impact of chemical processes has now opened new windows of opportunity for bio‐based catalysts. In this paper a highly active bio‐based catalyst of vitamin B₁₂ supported on graphene oxide nanosheets is reported for the selective aerobic oxidation of alcohols to the corresponding carbonyl compounds. Operational simplicity, mild reaction conditions, high yield and selectivity, non‐hazardous nature, commercial availability and affordability are the main advantages of this novel catalytic system.