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[en] Energy flow and C-Hmethyl and C-Hring bond dissociations in vibrationally excited toluene in the collision with N2 and O2 have been studied by use of classical trajectory procedures. The energy lost by the vibrationally excited toluene upon collision is not large and it increases slowly with increasing total vibrational energy content between 5,000 and 45,000 cm-1. Intermolecular energy transfer occurs via both of V-T and V-V transfers. Both of V-T and V-V transfers increase as the total vibrational energy of toluene increases. When the total energy content ET of toluene is sufficiently high, either C-H bond can dissociate. The C-Hmethyl dissociation probability is higher than the C-Hring dissociation probability, and that in the collision with N2 is larger than with O2
[en] Polysilanes with sterically bulky substituents, -(2-(R1R2-phenyl)propyl)Si(R3)-, such as poly(2-phenylpropyl)(n-hexyl)silane (R1=R2=H, R3=n-hexyl) were prepared by Wurtz-type coupling reactions with Na using a sonochemical method. The high-intensity ultrasound provided the formation of high quality Na dispersion in toluene and its active surface which was important for the synthesis of polysilanes in Wurtz-type coupling reaction was freshly and continuously regenerated during the process. The polysilanes products were mixtures of high molecular weight polymers with Mw of ∼106 and low molecular weight polymer was greatly influenced by the substituents R3, directly attached to Si. On the contrary, changes on substituents (R1, R2) gave no influences at all. Overall yields for polysilanes were 75-99% in general but high molecular weight polysilanes were obtained as a major product when substituent R3 is n-hexyl group and low molecular weight polysilanes were obtained as a major product when substituent R3 is cyclohexyl and 2-phenylethyl groups. Effects of reaction conditions to polysilane yields were investigated
[en] Energy transfer and bond dissociation of C-Hmethyl and C-Hring in excited toluene in the collision with H2 and D2 have been studied by use of classical trajectory procedures at 300 K. Energy lost by the vibrationally excited toluene to the ground-state H2/D2 is not large, but the amount increases with increasing vibrational excitation from 5000 and 40,000 cm.1. The principal energy transfer pathway is vibration to translation (V-T) in both systems. The vibration to vibration (V-V) step is important in toluene + D2, but plays a minor role in toluene + H2. When the incident molecule is also vibrationally excited, toluene loses energy to D2, whereas it gains energy from H2 instead. The overall extent of energy loss is greater in toluene + D2 than that in toluene + H2. The different efficiency of the energy transfer pathways in two collisions is mainly due to the near-resonant condition between D2 and C-H vibrations. Collision-induced dissociation of C-Hmethyl and C-Hring bonds occurs when highly excited toluene (55,000-70,400 cm-1) interacts with the ground-state H2/D2. Dissociation probabilities are low (10-5∼10-2) but increase exponentially with rising vibrational excitation. Intramolecular energy flow between the excited C-H bonds occurring on a subpicosecond timescale is responsible for the bond dissociation
[en] This paper reports that world styrene demand, paced by a near doubling of combined requirements in East Asia and Oceania, could reach 19.3 million metric tons by 2000, an average growth rate of 3.7%/year. So concludes Chem Systems Inc., Tarrytown, N.Y., in a study of world styrene markets through the end of the century. Pacific Rim styrene production and consumption throughout the 1990s are predicted to make up increasingly larger shares of world markets, while demand and production lag in the U.S. and western Europe. Demand and capacity in other parts of the world will grow in real terms, increasing combined market shares only slightly. Most of the increase will be driven by demand in East Asia and Oceania, where consumption by century's end is expected to increase 4.48 million metric tons from 2.25 million tons in 1991. Meantime, Japan's styrene demand in 2000 is projected at 2.64 million tons, a 500,000 ton increase from 1991 demand but a net market loss of 1.9%
[en] Intramolecular energy flow and C-Hmethyl and C-Hring bond dissociations in vibrationally excited toluene in the collision with HF have been studied by use of classical trajectory procedures. The energy lost by the vibrationally excited toluene upon collision is not large and it increases slowly with increasing total vibrational energy content between 20,000 and 45,000 cm-1. Above the energy content of 45,000 cm-1, however, energy loss decreases. Furthermore, in the highly excited toluene, toluene gains energy from incident HF. The temperature dependence of energy loss is negligible between 200 and 400 K. Energy transfer to or from the excited methyl C-H bond occurs in strong collisions with HF transferring relatively large amount of its translational energy (>>kBT) in a single step, whereas energy transfer to the ring C-H bond occurs in a series of small steps. When the total energy content ET of toluene is sufficiently high, either C-H bond can dissociate. The C-Hmethyl dissociation probability is higher than the C-Hring dissociation probability. The dissociation of the ring C-H bond is not the result of the intermolecular energy flow from the direct collision between the ring C-H and HF but the intramolecular flow of energy from the methyl group to the ring C-H stretch. The C-Hring···HF interaction is not important in transferring energy and in turn bond dissociation
[en] A novel compound, 6,6'-(butane-1,1-diyl)bis(4-methylbenzene-1,2-diol) (BMB), was synthesized through an acid-catalyzed condensation reaction between 4-methylcatechol (HPC) and butyraldehyde. When evaluated by the Rancimat and deep frying methods, BMB exhibited a stronger antioxidant activity than TBHQ. Its DPPH radical scavenging activity was also fairly higher than TBHQ, but lower compared to its mother phenol, HPC, due to its relative ease of binding DPPH•. BMB had the strongest scavenging ability of the 4-methylcatechol analogues reported to date. It could be used effectively to retard lipid peroxidation in both moderate and high temperature food preparations.
[es]Un nuevo compuesto, 6,6'-(butano-1,1-diil)bis(4-metilbenceno-1,2-diol) (BMB) fue sintetizado mediante una reacción de condensación catalizada por ácido entre el 4-metilcatecol (HPC) y el butiraldehído. Cuando se evaluó mediante los métodos Rancimat y de fritura, el BMB mostró una actividad antioxidante más fuerte que el TBHQ. Su actividad de eliminación de radicales DPPH también fue bastante mayor que la del TBHQ, pero menor en comparación con el fenol de partida, HPC, debido a su relativa facilidad para unirse a DPPH• .BMB tiene una actividad de eliminación más fuerte que los análogos de 4-metilcatecol reportados hasta la fecha. Podría usarse eficazmente para retardar la peroxidación de lípidos en la preparación de alimentos a temperatura moderada y alta.
[en] A photonic crystal fibre with hollow core filled with toluene is considered as a new system for coherent supercontinuum generation. The dispersion characteristics are studied for various geometrical parameters of photonic crystal fibres. Two structures with lattice constant 2 μm, filling factors d/Λ 0.3 and 0.35 and toluene core of diameters of 3.34 and 3.23 μm have flat dispersion in the near infrared range. The structure with d/Λ = 0.3 has all-normal dispersion characteristics in whole near-infrared wavelength range, while the second structure (d/Λ = 0.35) has anomalous dispersion for wavelengths longer than 1.5 μm. Although confinement losses in the considered structures are as high as 0.4 dB cm−1, we show that the generation of coherent supercontinuum in the range 1.0–1.7 μm with the pulse energy conversion of 16% is feasible in 4 cm long fibre samples with standard fibre femtosecond lasers. (paper)
[en] Green and Kubo showed that the phenomenological coefficients describing many transport processes and time dependent phenomena in general could be written as integrals over a certain type of function called a time correlation function. The Green-Kubo formulas are the formal expressions for hydrodynamic field variables and some of the thermodynamic properties in terms of the microscopic variables of an N-particle system. The identification of microscopic expressions for macroscopic variables is made by a process of comparison of the conservation equations of hydrodynamics with the microscopic equations of change for conserved densities. The importance of these formulas is three-fold: they provide an obvious method for calculating transport coefficients using computer simulation, a convenient starting point for constructing analytic theories for non-equilibrium processes, and an essential information for designing non-equilibrium molecular dynamics (NEMD) algorithm.
[en] We present a shape memory polymer (SMP) honeycomb with tuneable and shape morphing mechanical characteristics. Kirigami (Origami with cutting allowed) techniques have been used to design and manufacture the honeycomb. The cellular structure described in this work has styrene SMP hinges that create the shape change and the deployment actuation. To create a large volumetric deployment, the Kirigami open honeycomb configuration has been designed by setting an initial three-dimensional re-entrant auxetic (negative Poisson’s ratio) configuration, while the final honeycomb shape assume a convex (positive Poisson’s ratio) layout. A model was developed to predict the shape change of the structure, and compared to experimental results from a demonstrator honeycomb deployment test. (letter)
[en] The electronic spectrum of the benzene-toluene hetero-dimer ion is measured in the 380-1400 nm region. The spectrum shows intense bands around 1175 and 670 nm and a weaker band around 920 nm, which correspond to charge resonance (CR) bands of homo-dimer ions. The observation indicates that the positive charge stays on the benzene part in some probability, although the ionization potential of benzene is 0.4162 eV higher than that of toluene. A local excitation (LE) band is observed around 420 nm, where a πrelata of a relationπ transition is locally excited in the charged benzene or toluene molecule. On the basis of the positions of the CR-like bands, as well as the intensity of the LE band relative to that of homo-dimer ions, the probability of finding the charge on the benzene molecule is analyzed to be approximately 36%. (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)