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The influences of unresolved turbulent fluctuations in composition and temperature (turbulencechemistry interactions-TCI) on heat release, flame structure, and emissions are explored in unsteady Reynolds-averaged simulations for a heavy-duty diesel engine at four operating conditions. TCI are isolated and quantified by comparing results from a transported probability density function (PDF) method with those from a model that neglects the influence of fluctuations on local mean reaction rates (a well-stirred-reactor-WSR-model), with all other aspects of the modeling being the same (e.g., spray model, gas-phase chemical mechanism, and soot model). The simulations feature standard fuel-spray and turbulence models, skeletal-level gas-phase chemistry, and a semi-empirical two-equation soot model. Computed pressure and heat-release traces, turbulent flame structure, and emissions from the WSR and PDF models show marked differences, with the PDF-model results being in closer agreement with experiment in most cases. The soot results are especially striking. Computed soot levels from the PDF model are within a factor of five of the measured engine-out particulate matter, and computed soot levels from the WSR and PDF models differ by up to several orders of magnitude, with the PDF-model results being in much closer agreement with experiment. The results show that TCI are important in compression-ignition engines, and that accurate accounting for turbulent fluctuations is at least as important as accurate kinetic rate parameters in the gas-phase chemistry and soot models.

Structural and electronic properties for a series of silicon-substituted benzenes (C n Si m H6, where n = 0−6, m = 0−6, and n + m = 6) are studied through density functional theory calculations. Benzene is found to sustain its planarity up to two Si substitutions for all isomers. For three Si substitutions, only the 1,3,5-alternate structure (6) is planar, while for four Si substitution, only the 2,3,5,6 structure (10) is planar. Further Si substitution makes all the isomers for the rings nonplanar, which eventually leads to the fully puckered C 3v structure for hexasilabenzene (13). The reorganization energies for these molecules are sufficiently low to be favorably utilized for hole conduction. All the molecules form very stable full-sandwich and half-sandwich complexes of the type η6-(C n Si m H6)2Cr and η6-(C n Si m H6)Cr(CO)3. The binding energies for these complexes increase with increase in the number of Si atoms in the rings. Strategies are proposed for experimental design of extended sheets of silicenes and mixed C/Si graphenes through transition-metal complexation of the six-membered rings.

In this work, we have investigated the effects of denaturing agents, guanidine hydrochloride (GnHCl) and temperature, on the overall structure, domain-I, and domain-III of human serum albumin (HSA) using circular dichroism (CD) spectroscopy and steady-state, time-resolved fluorescence spectroscopy. We have tagged Cys-34 of HSA, located at domain-I, using N -(7-dimethylamino-4-methylcoumarin-3-yl)iodoacetamide and Tyr-411 of HSA, located at domain-III, using p -nitrophenyl coumarin ester, for this purpose. The CD spectroscopy studies reveal the overall denaturation of the protein. The denaturation follows the expected direction in which the protein is denatured with an increase in the concentration of GnHCl or temperature. The α-helicity of the native state of HSA was found to be 64.2%, and the minimum value of α-helicity was found to be 14.8% in the presence of 6 M GnHCl at room temperature. Steady-state emission studies were carried out on domain-I and domain-III of the protein using site-specific fluorescent tags. The degree of folding of the two domains at different combinations of temperature and GnHCl concentration was calculated and was found to follow a slightly different course of denaturation. Solvation dynamics was found to be quite different for these two domains. The domain-I of HSA has a maximum solvation time of 0.39 ns, and the solvation time tends to decrease with the action of either temperature or GnHCl. On the other hand, the domain-III of HSA showed a much higher solvation time (1.42 ns) and does not show any regular change at higher temperatures or in the presence of GnHCl. This difference could be attributed to the different microenvironment inside the protein cores of the two domains.