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11.
We show how the Landau–Pomeranchuk–Migdal effect on photon production rates in a quark–gluon plasma can be derived via the usual Boltzmann equation. To do this, we first derive the electromagnetic polarization tensor using linear response theory, and then formulate the Boltzmann equation including the collisions mediated by soft gluon exchanges. We then identify the resulting expression for the production rate with that obtained by the field-theoretic formalism recently proposed by Arnold, Moore and Yaffe. To illustrate the LPM effect we solve the Boltzmann equation in the diffusion approximation. 相似文献
12.
Most adhesives and binders, including bitumen for asphalt mixture production, are presently produced from petrochemicals after
the refining of crude oil. The fact that crude oil reserves are a finite resource means that in the future, it may become
necessary to produce these materials from alternative and probably renewable sources. Suitable resources of this kind may
include polysaccharides, plant oils and proteins. This paper deals with the synthesis of polymer binders from monomers that
could, in future, be derived from renewable resources. These binders consist of polyethyl acrylate (PEA) of different molecular
weight, polymethyl acrylate (PMA) and polybutyl acrylate (PBA), which were synthesised from ethyl acrylate, methyl acrylate
and butyl acrylate, respectively, by atom transfer radical polymerisation. The rheological properties of these binders were
determined by means of oscillatory testing using a dynamic shear rheometer and combinations of stress/strain, temperature
and frequency sweeps. The results indicate that PEA can be produced to have rheological properties similar to that of ‘soft’
100/150 penetration grade bitumen, PMA with similar rheological properties to that of ‘hard’ 10/20 penetration grade bitumen,
while PBA, due to its highly viscous nature and low dynamic moduli, cannot be used on its own as a binder. The synthetic polymers
were found to be thermo-rheologically simple, and the shift factors, used to produce the dynamic moduli master curves, were
found to fit an Arrhenius function. 相似文献
13.
A. Biedunkiewicz N. Gordon J. Straszko S. Tamir 《Journal of Thermal Analysis and Calorimetry》2007,88(3):717-722
Results of research work on oxidation of TiC/C nano-composites in air and under non-isothermal conditions are presented.
The oxidation of nano-crystalline titanium carbide as well as its carbon composites were studied using TG-DSC method in dry
air atmosphere. The investigated samples were as follows: commercial TiC nano-powders from Alfa Aesar (80 nm) and carbon composites
including nano-crystalline TiC (30 nm and 50, 10, 3 mass% of carbon in matrix). The measurements were executed in the Setaram
thermoanalyser TG-DSC 92-15 in non-isothermal conditions, with mass samples of 30±0.2 mg and constant heating rate in the
range 2–10 K min−1. 相似文献
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17.
Claudio Arato E. Kendall Pye Gordon Gjennestad 《Applied biochemistry and biotechnology》2005,123(1-3):871-882
Processes that produce only ethanol from lignocellulosics display poor economics. This is generally overcome by constructing
large facilities having satisfactory economies of scale, thus making financing onerous and hindering the development of suitable
technologies. Lignol Innovations has developed a biorefining technology that employs an ethanol-based organosolv step to separate
lignin, hemicellulose components, and extractives from the cellulosic fraction of woody biomass. The resultant cellulosic
fraction is highly susceptible to enzymatic hydrolysis, generating very high yields of glucose (>90% in 12–24h) with typical
enzyme loadings of 10–20 FPU (filter paper units)/g. This glucose is readily converted to ethanol, or possibly other sugar
platform chemicals, either by sequential or simultaneous saccharification and fermentation. The liquor from the organosolv
step is processed by well-established unit operations to recover lignin, furfural, xylose, acetic acid, and a lipophylic extractives
fraction. The process ethanol is recovered and recycled back to the process. The resulting recycled process water is of a
very high quality, low BOD5, and suitable for overall system process closure. Significant benefits can be attained in greenhouse gas (GHG) emission reductions,
as per the Kyoto Protocol. Revenues from the multiple products, particularly the lignin, ethanol and xylose fractions, ensure
excellent economics for the process even in plants as small as 100 mtpd (metric tonnes per day) dry woody biomass input—a
scale suitable for processing wood residues produced by a single large sawmill. 相似文献
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19.
Allen I. Cohen
Louis Gordon
《Talanta》1961,7(3-4):195-211Studies have been made of the distribution behaviour of tracers with alkaline earth sulphates, using the technique of precipitation from homogeneous solution. The co-precipitation of strontium with barium sulphate and of lead, lanthanum, and yttrium, separately, with barium sulphate, and with strontium sulphate, were investigated. Although there was qualitative correlation between the observed values of the distribution coefficient and the theoretical solubility product ratios for each of the binary systems studied, the divergence between theory and observation was so great that it seems unlikely that there is any quantitative correlation. 相似文献
20.
Häussermann U Amerioun S Eriksson L Lee CS Miller GJ 《Journal of the American Chemical Society》2002,124(16):4371-4383
This work presents a detailed, combined experimental and theoretical study on the structural stability of s-p bonded compounds with the BaAl4 structure type (space group I4/mmm, Z = 2) as part of a broad program to investigate the complex questions of structure formation and atomic arrangements in polar intermetallics. From ab initio calculations employing pseudopotentials and a plane wave basis set, we extracted optimized structural parameters, binding energies, and the electronic structure of the systems AeX(III)4, AeX(II)2X(IV)2, AeX(II)2X(III)2 (Ae = Ca, Sr, Ba; X(II) = Mg, Zn; X(III) = Al, Ga; X(IV) = Si, Ge). For all systems we found a pronounced pseudo-gap in the density of states separating network X42- bonding from antibonding electronic states that coincides with the Fermi level for an electron count of 14 electrons per formula unit, the optimum value for stable BaAl4-type polar intermetallics. However, the synthesis and structural characterization (from X-ray single crystal and powder diffraction data) of the new compounds AeZn2-Al2+, AeZn2-deltaGa2+delta (Ae = Ca, Sr, Ba; delta = 0-0.2) and AeMg0.9Al3.1, AeMg1.7Ga2.3 (Ae = Sr, Ba) manifested that electron deficiency is rather frequent for BaAl4-type polar intermetallics. The site preference for different "X" elements in the ternary systems was quantified by calculating "coloring energies", which, for some systems, was strongly dependent on the size of the electropositive Ae component. The Ae2+ cations decisively influence the nearest neighbor distances in the encapsulating polyanionic networks X4(2-) and the structures of these networks are surprisingly flexible to the size of the Ae component without changing the overall bonding picture. A monoclinically distorted variant of the BaAl4 structure occurs when the cations become too small for matching the size of encapsulating X4(2-) cages. An even larger size mismatch leads to the formation of the EuIn4 structure type. 相似文献