Direct synthesis of polyaromatic chains of tribenzopentaphene copolymers through cyclodehydrogenation of their poly‐tetraphenylbenzene precursors

Three polyaromatic‐based polymers are reported to contain co‐monomers of trapezoidal tribenzopentaphene (TBP) polycyclic aromatic hydrocarbons. The synthetic strategy consists of initially making highly soluble tetraphenylbenzene copolymers 4a–c , followed by a cyclodehydrogenation/aromatization reaction to obtain target polymers 5a–c . The polymers were characterized by gel permeation chromatography, FT‐IR, UV‐vis, emission, ¹H‐, and ¹³C‐nuclear magnetic resonance spectroscopy. The target polymers 5a–c reveal emission spectra in the range of 430–480 nm; thus, qualifying them to act as blue emitters. Investigation of the polymers optical properties and their correlation with density functional theory calculations suggest a distorted TBP core from planarity caused by the introduction of a dodecyl group at its wide edge. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3565–3572     

Laser-induced breakdown spectroscopic studies of marbles

We present laser-induced breakdown spectroscopic studies of variety of marbles extracted from Quetta region of Boluchistan, Pakistan using a Nd:YAG laser (532 nm) in conjunction with LIBS 2000 detection system. The emission spectra of Onyx (white spot) and Quetta Green Marble samples have been recorded as a function of laser irradiance. The elemental composition and their relative abundance in each sample are fond to be quite different. In Onyx (white spot), calcium dominates while in the Quetta Green marble magnesium is the dominant element. In addition the effect of the laser irradiance on the emission intensity, width and shift of the transition lines have been studied.     

A validation of the p-SLLOD equations of motion for homogeneous steady-state flows

A validation of the p-SLLOD equations of motion for nonequilibrium molecular dynamics simulation under homogeneous steady-state flow is presented. We demonstrate that these equations generate the correct center-of-mass trajectory of the system, are completely compatible with (and derivable from) Hamiltonian dynamics, satisfy an appropriate energy balance, and require no fictitious external force to generate the required homogeneous flow. It is also shown that no rigorous derivation of the SLLOD equations exists to date.     

Rheological and structural studies of linear polyethylene melts under planar elongational flow using nonequilibrium molecular dynamics simulations

We present various rheological and structural properties of three polyethylene liquids, C50H102, C78H158, and C128H258, using nonequilibrium molecular dynamics simulations of planar elongational flow. All three melts display tension-thinning behavior of both elongational viscosities, eta1 and eta2. This tension thinning appears to follow the power law with respect to the elongation rate, i.e., eta approximately epsilon(b), where the exponent b is shown to be approximately -0.4 for eta1 and eta2. More specifically, b of eta1 is shown to be slightly larger than that of eta2 and to increase in magnitude with the chain length, while b of eta2 appeared to be independent of the chain length. We also investigated separately the contribution of each mode to the two elongational viscosities. For all three liquids, the intermolecular Lennard-Jones (LJ), intramolecular LJ, and bond-stretching modes make positive contributions to both eta1 and eta2, while the bond-torsional and bond-bending modes make negative contributions to both eta1 and eta2. The contribution of each of the five modes decreases in magnitude with increasing elongation rate. The hydrostatic pressure shows a clear minimum at a certain elongation rate for each liquid, and the elongation rate at which the minimum occurs appears to increase with the chain length. The behavior of the hydrostatic pressure with respect to the elongation rate is shown to correlate with the intermolecular LJ energy from a microscopic viewpoint. On the other hand, R(ete)2 and R(g)2 appear to be correlated with the intramolecular LJ energy. The study of the effect of the elongational field on the conformation tensor c shows that the degree of increase of tr(c)-3 with the elongation rate becomes stronger as the chain length increases. Also, the well-known linear reaction between sigma and c does not seem to be satisfactory. It seems that a simple relation between sigma and c would not be valid, in general, for arbitrary flows.     

Structure formation under steady-state isothermal planar elongational flow of n-eicosane: a comparison between simulation and experiment

We use nonequilibrium molecular dynamics simulations to investigate the structural properties of an oriented melt of n-eicosane under steady-state planar elongational flow. The flow-induced structure was evaluated using the structure factor s(k) taken as the Fourier transform of the total pair correlation function g(r). We found that the equilibrium liquid structure factor is in excellent agreement with the one determined via x-ray diffraction. Moreover, a new x-ray diffraction experiment has been performed on a crystalline n-eicosane sample. The resulting intramolecular contribution to the structure factor was found to be in very good agreement with the simulated one at a high elongation rate, indicating the existence of a possible crystalline precursor structure.     

Enhanced efficiency and extended wavelength range of dye lasers operated with DCM

It is observed that the efficiency of the DCM dye dissolved in ethylene glycol benzyl alcohol can be enhanced if the dye is preheated at a temperature of 150 °C. Peak powers as high as 1.5 W have been achieved with a single-mode ring dye laser at 640 nm when pumped by 9 W (all lines) from an argon-ion laser. The wavelength region has been also extended beyond both ends of the tuning curve compared to a conventionally prepared DCM dye. Received: 3 September 1999 / Revised version: 9 December 1999 / Published online: 23 February 2000     

Influence of interfacial reaction and mobility ratio on the displacement of oil in a Hele-Shaw cell

A comparative experimental study was conducted to examine the effect of fluid-fluid interfacial reaction on immiscible displacements in a wide range of mobility ratios. The nonreactive fluid pair consisted of paraffin oil/decane mixtures and water. In order to formulate a reactive system, linoleic acid (10 mol/m³) was added to the oil and sodium hydroxide (25 mol/m³) was added to the water. The experiments were performed in a square Hele-Shaw cell, simulating a quarter of a reversed five-spot pattern. Displacement patterns produced by reactive and nonreactive fluid pair systems were fundamentally different from each other. The recovery in the reactive system was generally higher than in the non-reactive system. The recovery at breakthrough for both the reactive and the non-reactive systems increased with a decrease in the viscosity of oil. In the non-reactive system, the recovery at one hour after breakthrough increased with the decrease in oil viscosity and became constant at 63% when the oil viscosity reached 6.86 mPa · s. In the reactive system the recovery at one hour after breakthrough was nearly 100% regardless of oil phase viscosity. When the oil viscosity was lower than the viscosity of the displacing phase (favorable mobility ratio), the recovery percentage was high. However, the jagged character of the displacement front characteristic of the reactive system was still preserved.     

Spectroscopic studies of laser induced aluminum plasma using fundamental,second and third harmonics of a Nd:YAG laser

In the present work, we have studied the spatial evolution of the aluminum plasma produced by the fundamental (1064 nm), second (532 nm) and third (355 nm) harmonics of a Q-switched pulsed Nd:YAG laser. The experimentally observed line profiles of neutral aluminum have been used to extract the excitation temperature using Boltzmann plot method whereas the electron number density has been determined from the Stark broadened profiles. Besides we have studied the variation of excitation temperature and electron number density as a function of laser irradiance at atmospheric pressure. In addition, we have performed quantitative analysis of photon absorption and vapor ionization mechanism at three laser wavelengths and estimated the inverse bremsstrahlung (IB) absorption and photoionization (PI) coefficients. The validity of the assumption of local thermodynamic equilibrium is discussed in the light of the experimental results.     

f-Dominance of the Pomeron in Reggeon Field Theory

A Reggeon Field Theory (RFT) which incorporates the Pomeron and thef-pole is presented. The constrains on the renormalization group β-functions imposed by thef-dominance of the Pomeron are derived. We show that these constrains are satisfied by the RFT at least up to third order in the coupling constants.     

Optimal scheme for estimating a pure qubit state via local measurements

We present the optimal scheme for estimating a pure qubit state by means of local measurements on N identical copies. We give explicit examples for low N. For large N, we show that the fidelity saturates the collective measurement bound up to order 1/N. When the signal state lays on a meridian of the Bloch sphere, we show that this can be achieved without classical communication.