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71.
F. Migliorini K. A. Thomson G. J. Smallwood 《Applied physics. B, Lasers and optics》2011,104(2):273-283
The optical properties of soot, in particular the propensity of soot to absorb and scatter light as a function of wavelength,
are key parameters for the correct interpretation of soot optical diagnostics. An overview of the data available in the literature
highlights the differences in the reported optical properties of aging soot. In many cases, the properties of mature soot
are used when evaluating in-flame soot but this assumption might not be suitable for all conditions and should be checked.
This need has been demonstrated by performed spectral resolved line-of-sight attenuation (Spec-LOSA) measurements on an ethylene/air
premixed and non-premixed flame. Transmission electron microscopy of thermophoretically sampled soot was also performed to
qualify the soot aging and to establish soot morphology in order to correct light extinction coefficients for the scattering
contribution. The measured refractive index absorption function, E(m)
λ
, showed a very strong spectral dependence which also varied with height above the burner for both flames. However, above
700 nm, the slope of the refractive index function was near zero for both flames and all measurement heights. The upper visible
and near infrared wavelengths are therefore recommended for soot optical measurements. 相似文献
72.
M. Köhler K. P. Geigle W. Meier B. M. Crosland K. A. Thomson G. J. Smallwood 《Applied physics. B, Lasers and optics》2011,104(2):409-425
Computational fluid dynamics (CFD) modelers require high-quality experimental data sets for validation of their numerical
tools. Preferred features for numerical simulations of a sooting, turbulent test case flame are simplicity (no pilot flame),
well-defined boundary conditions, and sufficient soot production. This paper proposes a non-premixed C2H4/air turbulent jet flame to fill this role and presents an extensive database for soot model validation. 相似文献
73.
K. A. Thomson K. P. Geigle M. Köhler G. J. Smallwood D. R. Snelling 《Applied physics. B, Lasers and optics》2011,104(2):307-319
To investigate the transient change of soot optical properties resulting from pulsed laser heating of soot in a cooled exhaust
plume we have simultaneously performed cw light extinction at 405 and 830 nm and elastic light scattering at 1064 nm. A reversible
increase to the 830-nm light extinction of up to 7%, observed during the time period where the soot was hot, suggests a temperature-dependent
light absorption refractive index function, E(m
λ
). At low fluence, small permanent increases of E(m
λ
) of <2% were also observed. 405-nm extinction measurements revealed that the soot likely contained material which continued
to absorb 405-nm radiation when desorbed, thus complicating measurement interpretation. 1064-nm light scattering measurements
showed a gradual decrease of scattering propensity with increasing laser fluence up to the point of material loss, which is
consistent with the expected decrease of the structure factor of the soot aggregates as they expand. It is concluded that
variations of the optical properties are occurring at the time of laser-induced incandescence (LII) emission, which should
be accounted for in time-resolved LII measurement interpretation. 相似文献
74.
75.
Z. Liu R. BrandtO. Hellwig S. FlorezT. Thomson B. TerrisH. Schmidt 《Journal of magnetism and magnetic materials》2011,323(12):1623-1626
We present the measurements of the picosecond magnetization dynamics of Co/Pd multilayer films. The dynamic magnetization properties of sputtered multilayer films were analyzed as a function of Co layer thicknesses and applied bias field. Both the eigenfrequencies of the magnetization precession in the multilayers and the associated Gilbert damping exhibit extreme sensitivity to the magnetic layer thickness on an atomic monolayer scale. The eigenfrequency increases more than threefold when the Co thickness decreases from 7.5 to 2.8 Å, mainly due to the changes in effective saturation magnetization and perpendicular anisotropy constant. A concomitant 2.6-fold increase in the damping of the oscillations is observed and attributed to stronger interface dissipation in thinner Co layers. In addition, we introduce a quasi-1D micromagnetic model in which the multilayer stack is described as a one-dimensional chain of macrospins that represent each Co layer. This model yields excellent agreement with the observed resonance frequencies without any free parameters, while being much simpler and faster than full 3D micromagnetic modeling. 相似文献
76.
Stephen G. Davies Ai M. Fletcher Gesine J. Hermann Giovanna Poce Paul M. Roberts Andrew D. Smith Miles J. Sweet James E. Thomson 《Tetrahedron: Asymmetry》2010,21(13-14):1635-1648
The doubly diastereoselective conjugate addition of the antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide to a range of enantiopure N-enoyl oxazolidin-2-ones has been used as a mechanistic probe to determine that the reactive conformation is the anti-s-cis form. The β-amino carbonyl products resulting from these conjugate addition reactions are useful templates for further elaboration into an α,β,α-pseudotripeptide. 相似文献
77.
The reaction mechanism of an analogue system of the molybdenum oxotransferases was investigated at the density functional (B3P86) level of theory. Kinetic measurements by Schultz and Holm suggest that the reaction MoO(2)(t-BuL-NS)(2) + X --> MoO(t-BuL-NS)(2) + OX (t-BuL-NS = bis(4-tert-butylphenyl)-2-pyridylmethanethiolate(1-)) occurs through an associative transition state. Our results on the model reaction, MoO(2)(SCH(2)CHNH)(2) + P(CH(3))(3) --> MoO(SCH(2)CHNH)(2) + OP(CH(3))(3), support this hypothesis, and indicate that this reaction proceeds through a two-step mechanism via an associative intermediate. The DeltaH(++) for the first, and rate-determining, step was predicted to be 9.4 kcal/mol, and DeltaH(++) for the second step (release of the OP(CH(3))(3) product) was predicted to be 3.3 kcal/mol. These results are in good agreement with the experimental system, for which the rate determining DeltaH(++) = 9.6(6) kcal/mol. Shultz and Holm's experimental model undergoes a significant ligand rearrangement in the oxo transfer reaction: the reactant, MoO(2)(t-BuL-NS)(2), has a trans-S arrangement of the ligands, while the product, MoO(t-BuL-NS)(2), has a trans-N arrangement. To investigate the driving force behind the ligand rearrangement, four model compounds, that systematically removed the unsaturation at the N and the chelate character of the ligands, were modeled at the B3P86 level of theory. For all models of the dioxo species, the trans-N isomer was higher in energy than the trans-S isomer. The analysis of these results indicated that a trans influence accounts for approximately 16% of the energy difference, the unsaturation at the nitrogens accounts for approximately 26%, and the ring strain from the chelator accounts for approximately 58% of the energy difference between the two isomers (trans-N and trans-S). For all models of the monooxo species, only the trans-N species was a stable geometry. Therefore, for the reverse oxo transfer reaction, ligand rearrangement must occur after or during the attack of the OX substrate. 相似文献
78.
Burke W Acheson L Botkin J Bridges K Davis A Evans J Frias J Hanson J Kahn N Kahn R Lanier D Pinsky LE Press N Lloyd-Puryear MA Rich E Stevens N Thomson E Wartman S Wilson M 《Community genetics》2002,5(2):138-146
The Genetics in Primary Care (GPC) project is a USA national faculty development initiative with the goal of enhancing the training of medical students and primary care residents by developing primary care faculty expertise in genetics. Educational strategies were developed for the project by an executive committee with input from an advisory committee, comprising individuals with primary care, medical education and genetics expertise. These committees identified the key issues in genetics education for primary care as (1) considering inherited disease in the differential diagnosis of common disorders; (2) using appropriate counseling strategies for genetic testing and diagnosis, and (3) understanding the implications of a genetic diagnosis for family members. The group emphasized the importance of a primary care perspective, which suggests that the clinical utility of genetic information is greatest when it has the potential to improve health outcomes. The group also noted that clinical practice already incorporates the use of family history information, providing a basis for discussing the application of genetic concepts in primary care. Genetics and primary care experts agreed that educational efforts will be most successful if they are integrated into existing primary care teaching programs, and use a case-based teaching format that incorporates both clinical and social dimensions of genetic disorders. Three core clinical skills were identified: (1) interpreting family history; (2) recognizing the variable clinical utility of genetic information, and (3) acquiring cultural competency. Three areas of potential controversy were identified as well: (1) the role of nondirective counseling versus shared decision-making in discussions of genetic testing; (2) the intrinsic value of genetic information when it does not influence health outcomes, and (3) indications for a genetics referral. The project provides an opportunity for ongoing discussion about these important issues. 相似文献
79.
The chemo- and enantioselective reduction of ethyl 4-chloroacetoacetate and the diastereoselective conjugate addition of enantiopure lithium N-benzyl-N-(α-methylbenzyl)amide to an α,β-unsaturated ester have been used as the key steps in the total asymmetric syntheses of (+)-negamycin (in 13 steps and 24% overall yield), (+)-3-epi-negamycin (in 13 steps and 10% overall yield) and sperabillin C (in 17 steps and 13% overall yield) from commercially available starting materials. 相似文献
80.
Stephen G. Davies Ai M. FletcherDeri G. Hughes James A. LeePaul D. Price Paul M. RobertsAngela J. Russell Andrew D. SmithJames E. Thomson Oliver M.H. Williams 《Tetrahedron》2011,67(51):9975-9992
The conjugate addition of an enantiopure lithium amide to a ζ-hydroxy-α,β-unsaturated ester followed by a one-pot ring-closure/N-debenzylation protocol has been used in the asymmetric syntheses of (S)-coniine and (R)-δ-coniceine (isolated as the corresponding hydrochloride salts), and (R,R)-1-(hydroxymethyl)octahydroindolizine (the bicyclic fragment of stellettamides A-C). 相似文献