Enhanced emission from single component organic core-shell nanoparticles

By one-step mixed-solvent mediated approach, we have prepared fluorescent organic core-shell nanoparticles with an oligomer (1) derived from the Schiff base condensation reaction of 2,6-diformyl-4-methylphenol and o-phenylenediamine at room temperature. The core and shell structures are generated by the same oligomer (1) featuring the aggregation structure in core different from that in shell. The radial packing factor distribution of oligomer cluster depending on the solvent interaction in the time of nucleation is mainly responsible for the single component core-shell formation. Different morphologies of the core-shell nanospheres (CSNS) and core-shell nanohemispheres (CSNHS) were generated simply by changing the concentration of 1 in chloroform-methanol mixed solvent (1:2). We observed that fluorescent emission from those core-shell nanoparticles is intense whereas as-synthesized oligomer (1) itself is non-fluorescent in dilute solution. The enhanced emission in the core-shell form with more than 50 times increase in fluorescent quantum yield vis-à-vis 1 is a remarkable feature of the study. As UV absorption spectra of nanoparticles are blue-shifted relative to their properties in solution, the observed strong emission in the solid state makes the oligomer an outstanding exception to a well-established rule based on the molecular exciton model. The core-shell nanoparticles have been characterized by FE-SEM, TEM, XRD, nanosecond (ns) time-resolved fluorescence dynamics, UV-Vis and fluorescence spectroscopy. The longer fluorescence lifetimes (tau) of core-shell nanoparticles (3.50 ns and 3.52 ns for CSNS and CSNHS respectively) than 1 as-synthesized (1.28 ns) implies that the formation of the nanoparticles restricts the rotation and vibration of the groups in the molecules. The factor that induces fluorescent enhancement of nanoparticles is mainly ascribed to the increase of radiative rate constant (k(r)) and simultaneous decrease of nonradiative rate constant (k(nr)).     

常压非热等离子体源及其在纺织整理中的应用

综述了常压介电屏蔽放电（DBD）产生的非热等离子体在纺织整理中的应用。描述了DBD在常压织物整理和等离子体化学中的许多潜在优势。DBD（无声放电）是一种非热等离子体放电,在较宽的温度和压力范围内操作简便。常压下,许多独立的细电流丝之间会发生电击穿,这些短暂的带有电子能量的微放电具有瞬时高压辉光放电性质,非常适合背景气体原子或分子的激发和离解。     

Highly Efficient and Reusable Polyaniline‐Supported Palladium Catalysts for Open‐Air Oxidative Heck Reactions under Base‐ and Ligand‐Free Conditions

Oxidative Heck reactions of arylboronic acids and alkenes are carried out in the presence of polyaniline‐supported palladium catalysts using air as a co‐oxidant to afford the Heck products with excellent yields and selectivities under base‐ and ligand‐free conditions. The catalyst was recovered by simple filtration and used for several cycles with consistent activity.     

A CAD approach for suppression of power supply noise and performance analysis of some multi-core processors in pre-layout stage

In modern system-on-chip, the number of transistors has grown exponentially. This requires an efficient electrical power distribution network for proper functioning of the chip. Voltages at different nodes with respect to the desired level may vary which correspond to generation of supply noise. This paper deals with the estimation and allocation of decoupling capacitance for reduction of supply noise at the pre-layout level. Usually, decoupling capacitors are placed near the noisy functional modules, which acts as local charge storing devices and effectively reduce the transients. In this work, analysis of various sources of supply noises has been performed. Depending on the amount of supply noise, the decoupling capacitance has been estimated and allocated with minimum increment in power consumption and propagation delay. We have considered 512-points, 1-k point, 2-k point and 4-k point Fast Fourier Transform processors and International Test Conference 1999 (b14 and b17) benchmark circuits as our test circuits. This work reports up to 51.9% reduction of peak supply noise at the cost of 0.48 and 1.44% increase in power consumption and delay respectively. This estimation and subsequent allocation of decoupling capacitances will help for more accurate design and implementation at the layout stage.

     

Tack and Green Strength of Blends of Bromobutyl and EPDM Rubbers. I. Unfilled Gum Blends

Polymer blends are gaining importance in recent years because they provide a compromise of properties. In this paper, tack and green strength of several blends of EPDM and bromobutyl rubbers (BIIR) have been studied over a wide range of temperaures, contact times and rates.

Tack increases with increase in contact time and with increase in contact temperature up to 47°C for a particular blend. At a much higher temperature the tack strength falls gradually. Green strength increases with increase in bromobutyl content and decreases with temperature. Tack index, a ratio of tack strength divided by the cohesive strength under the same geometry, decreases slowly with the test temperature. At a 50:50 ratio of BIIR:EPDM, the two rubbers form an interpenetrating network as observed under the phase contrast microscope.     

High-power Ar-N2transfer laser at 3577 Å

A peak laser power of 0.5 MW with an estimated efficiency of 0.2 percent has been obtained at 3577 Å from a mixture of 92 psia Ar and 8 psia N2which was excited by anE-beam of 400 A/cm²at 1.3 MeV in a 20-ns pulse. A saturation intensity of ∼100 kW/cm²was deduced and a beam divergence of 10 mrad was measured from the laser having a 10-cm gain length.     

Bubble size distribution in a flotation column

The bubbles that were generated in a flotation column were measured. The bubble size distributions were obtained both for air-water and air-water-coal systems. The size distribution pattern was fitted to different equations. It was found that the bubble size distribution in both the flotation and cleaning zones follows the Rosin-Rommler equation used to describe the particle size distribution in crushing. This study indicates that bubbles in the cleaning zone are always larger than those of the flotation zone and finer bubbles are generated when a mixture of frothers is used instead of individual frothers.     

Baeyer-Villiger rearrangement catalysed by titanium silicate molecular sieve (TS-1)/H2O2 system

Titanium silicate molecular sieve TS-1 has been found to be an efficient catalyst for Baeyer-Villiger (BV) oxidation of cyclic and aromatic ketones under triphase conditions (solid catalyst along with two immiscible liquid reactants in the absence of any cosolvent), using dilute H₂O₂. Reactions studied are the oxidation of cyclohexanone and acetophenone. Whereas in the case of cyclohexane,-caprolactone, a BV product along with hydroxy and diketones is formed, in the case of acetophenone, phenyl acetate, a BV product along witho- andp-hydroxyacetophenone is formed. The acidic nature of titanium peroxo species, stabilised by water, is proposed to be responsible for such reactions under triphasic reaction conditions.On leave from: Catalysis Division, Indian Institute of Petroleum, Dehradun 248 005, India.     

Fibers spun from blends of different molecular weights of polypropylene

Fibers spun from blends of small percentage of plastic grade polypropylene (HMPP) with fiber grade polypropylene (PP) are studied for drawing behavior. A factorial design of experiment is used for a two-stage drawing process with variables, such as percent of HMPP component, first stage draw ratio and temperature, and second stage temperature. Optimization is carried out for breaking stress and modulus of drawn filaments. Breaking stress of up to 0.74 GPa and initial modulus of 7.34 GPa is possible by such an optimization process. These properties are observed for 6% HMPP blend composition. Heat setting of drawn filaments show little changes up to 140°C heat-setting temperature. Large scale structural changes with rapid drop in mechanical properties is observed for 150-160°C heat-set samples.