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221.
222.
Sebastian M. Cioab? 《Discrete Mathematics》2006,306(16):1959-1964
For a graph G and k a real number, we consider the sum of the kth powers of the degrees of the vertices of G. We present some general bounds on this sum for various values of k. 相似文献
223.
Dominik Schröder Kai Banke Sebastian A. Kaiser Burak Atakan 《Proceedings of the Combustion Institute》2021,38(4):5567-5574
Fuel-rich combustion of methane in a homogeneous-charge compression-ignition (HCCI) engine can be used as a polygeneration process producing work, heat, and useful chemicals like syngas. Due to the inertness of methane, additives such as dimethyl ether (DME) are needed to achieve ignition at moderate inlet temperatures and to control combustion phasing. Because significant concentrations of DME are then needed, a considerable part of the fuel energy comes from DME. An alternative ignition promotor known from fuel-lean HCCI is ozone (O3). Here, a combined experimental and modelling study on the ignition of fuel-rich partial oxidation of methane/air mixtures at Φ = 1.9 with ozone and DME as additives in an HCCI engine is conducted. Experimental results show that ozone is a suitable additive for fuel-rich HCCI, with only 75 ppm ozone reducing the fuel-fraction of DME needed from 11.0% to 5.3%. Since ozone does not survive until the end of the compression stroke, the reaction paths are analyzed in a single-zone model. The simulation shows that different ignition precursors or buffer molecules are formed, depending on the additives. If only DME is added, hydrogen peroxide (H2O2) and formaldehyde (CH2O) are the most important intermediates, leading to OH formation and ignition around top dead center (TDC). With ozone addition, methyl hydroperoxide (CH3OOH) becomes very important earlier in the compression stroke under these fuel-rich conditions. It is then later converted to CH2O and H2O2. Thus, ozone is a very effective additive not only for fuel-lean, but also for fuel-rich combustion. However, the mechanism differs between both regimes. Because less of the expensive additives are needed, ozone could help improving the economics of a polygeneration process with fuel-rich operated HCCI engines. 相似文献
224.
Antony V. Wilson Timothy Nguyen Felix Brosi Xuefeng Wang Lester Andrews Sebastian Riedel Adam J. Bridgeman Nigel A. Young 《ChemInform》2016,47(14):no-no
Binary palladium fluorides from PdF to PdF6 are investigated by matrix‐isolation methods using thermal evaporation and laser ablation to generate Pd atoms for reaction with F2‐doped Ar and Ne matrices as well as neat F2 matrices. 相似文献
225.
Reaction products of laser‐ablated praseodymium atoms with fluorine in excess neon, argon, krypton, or neat fluorine at 4—10 K are investigated by IR spectroscopy and quantum chemical DFT and coupled‐cluster calculations. 相似文献
226.
Probing the Electronic Structure of Bacteriochlorophyll Radical Ions—A Theoretical Study of the Effect of Substituents on Hyperfine Parameters 下载免费PDF全文
In reaction centers (RCs) of photosynthesis, a light‐induced charge separation takes place creating radical cations and anions of the participating cofactors. In photosynthetic bacteria, different bacteriochlorophylls (BChl) are involved in this process. Information about the electronic structure of the BChl radical cations and anions can be obtained by measuring the electron spin density distribution via the electron–nuclear hyperfine interaction using EPR and ENDOR techniques. In this communication, we report isotropic hyperfine coupling constants (hfcs) of the BChl b and g radical cations and anions, calculated by density functional theory, and compare them with the more common radical ions of BChl a and with available experimental data. The observed differences in the computed hyperfine data are discussed in view of a possible distinction between these species by EPR/ENDOR methods. In addition, 14N nuclear quadrupole coupling constants (nqcs) computed for BChl a, b, g, and also for Chl a in their charge neutral, radical cation and radical anion states are presented. These nqcs are compared with experimental values obtained by ESEEM spectroscopy on several different radical ions. 相似文献
227.
Sebastian Pfadler Micha Löffler Friedrich Dinkelacker Alfred Leipertz 《Experiments in fluids》2005,39(2):375-384
The turbulence and temperature field of Bunsen-type turbulent lean methane/air flames has been investigated using planar laser Rayleigh scattering (PLRS) and stereo particle image velocimetry (stereo PIV). Temporally averaged reaction progress variable plots have been computed from PLRS measurements in order to provide a basis with regards to the verification of computational fluid dynamics (CFD) models. Turbulence was characterised by stereo PIV in one plane for all three velocity components. Averaged velocity fields have been calculated, as well as Reynolds-decomposed fluctuation vector fields. Conditioned root mean square (RMS) values of the turbulent fluctuations in terms of unburnt and burnt gas could be determined by making use of the information gained from a threshold setting procedure in the PIV raw images. Furthermore, several length scales were measured indirectly from PIV vector plots. In this context, all integral length scales being accessible with stereo PIV were computed separately for the burnt and unburnt regions and were compared to each other. It could be observed that all integral length scales increased in the burnt zone. Additionally, the conditioned Taylor and Kolmogorov lengths have been extracted from the PIV field data, derived either from the zero-radius curvature of the correlation function or from common turbulence theory relations. 相似文献
228.
Sebastian Mendrek Aleksandra Mendrek Hans-Juergen Adler Andrzej Dworak Dirk Kuckling 《Colloid and polymer science》2010,288(7):777-786
Temperature-sensitive poly(glycidol)-b-poly(N-isopropylacrylamide) block copolymers (PGl55PNIPAAmy) were synthesised and their aqueous solutions investigated by different methods including differential scanning calorimetry
(DSC), UV-VIS spectroscopy as well as dynamic and static light scattering. The cloud point temperature (T
c) depended on the composition of the investigated block copolymers and increased with decreasing length of the PNIPAAm block
in PGl55PNIPAAmy copolymers. In contrast, the enthalpy of phase separation of PNIPAAm segments measured by DSC decreased with decreasing length
of the PNIPAAm block in the polymer. These findings can be correlated with the behaviour of homo-PNIPAAm with similar molecular
weights indicating that the influence of PGl on the local environment and phase separation of PNIPAAm chains is similar to
the influence observed for PNIPAAm chains bearing different low molecular weight end group. Using DLS measurement, it was
shown that the aggregation process depended on the PGl/PNIPAAm block ratio. If the PGl/PNIPAAm ratio was low, stable core-shell
aggregates were formed. In contrast, the tendency to formation of large unstable, loose aggregates was observed for copolymers
with high PGl/PNIPAAm ratio. 相似文献
229.
Hoeb M Auernhammer M Schoell SJ Brandt MS Garrido JA Stutzmann M Sharp ID 《Langmuir : the ACS journal of surfaces and colloids》2010,26(24):18862-18867
We present an approach for the thermally activated formation of alkene-derived self-assembled monolayers on oxygen-terminated single and polycrystalline diamond surfaces. Chemical modification of the oxygen and hydrogen plasma-treated samples was achieved by heating in 1-octadecene. The resulting layers were characterized using X-ray photoelectron spectroscopy, thermal desorption spectroscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and water contact angle measurements. This investigation reveals that alkenes selectively attach to the oxygen-terminated sites via covalent C-O-C bonds. The hydrophilic oxygen-terminated diamond is rendered strongly hydrophobic following this reaction. The nature of the process limits the organic layer growth to a single monolayer, and FTIR measurements reveal that such monolayers are dense and well ordered. In contrast, hydrogen-terminated diamond sites remain unaffected by this process. This method is thus complementary to the UV-initiated reaction of alkenes with diamond, which exhibits the opposite reactivity contrast. Thermal alkylation increases the range of available diamond functionalization strategies and provides a means of straightforwardly forming single organic layers in order to engineer the surface properties of diamond. 相似文献
230.
Jannis W. Ochsmann Sebastian Lenz Sebastian G. J. Emmerling Ralf S. Kappes Sebastian K. Nett Maria C. Lechmann Stephan V. Roth Jochen S. Gutmann 《Journal of polymer science. Part A, Polymer chemistry》2010,48(14):1569-1573
Thin films of PS-b-PEO block copolymers were utilized as structured reservoirs for localized nanoscale precipitation reactions. By consecutively immersing the film into solutions of thioacetamide and cadmium chloride, we were able to obtain a monolayer of cadmium sulfide nanostructures on top of the block copolymer film. AFM and grazing incidence small angle X-ray scattering revealed spherical nanostructures (d = 15 nm) corresponding to the dimensions given by the block copolymer film. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1569–1573, 2010 相似文献