The effects of strain and curvature on the mass burning rate of premixed laminar flames

The Markstein number characterizes the effect that flame stretch has on the burning velocity. Different expressions for this number are deduced from integral analysis. According to a phenomenological law, the Markstein number can be separated into a part for the curvature of the flame and a part for the straining of the flow. This separation is analysed here. It appears that the Markstein number for curvature and the combined one for both curvature and strain are unique. It is, however, not possible to introduce a separate and unique Markstein number for the flow straining that can be used to describe its influence in different combustion situations. The theoretical and numerical analysis is applied to flat steady counterflow flames as well as to steady, imploding and expanding spherical flames.     

Experimental and numerical determination of heat release in counterflow premixed laminar flames

This paper presents an experimental and numerical study of heat release in atmospheric laminar counterflow premixed flames. The measurements are based on simultaneous planar laser-induced fluorescence (PLIF) of OH and HCHO. These measurements are compared to numerical results obtained using detailed chemistry and multicomponent transport properties. A low Mach number formulation along the stagnation streamline is employed to describe the reactive flow. The conservation equations are completed with CHEMKIN and EGLIB packages. They are solved using finite differences, Newton iterations, and an adaptive gridding technique. The comparison is done along the burner axis for both, maximum heat release location and heat release profile width. It is shown that the product of OH and HCHO concentrations yields a result closely related to the heat release. These comparisons lead to the conclusion that the experimental method used seems to be a good tool for the determination of heat release in flames.     

磁性隧道结热稳定性的x射线光电子能谱研究

通过XPS等微观分析手段证实了磁性隧道结在高温退火后，反铁磁层中的Mn元素扩散到被钉 扎铁磁层及势垒层中，破坏了势垒层/铁磁层界面，从而导致了磁性隧道结高温退火后TMR的 下降.然而在反铁磁层和被钉扎铁磁层之间插入一层纳米氧化层后，Mn的扩散得到了抑制， 使磁性隧道结的热稳定性得以提高. 关键词： 磁性隧道结 纳米氧化层 x射线光电子能谱     

An investigation of flame zones and burning velocities of laminar unconfined methane-oxygen premixed flames

Numerical and experimental investigations of unconfined methane-oxygen laminar premixed flames are presented. In a lab-scale burner, premixed flame experiments have been conducted using pure methane and pure oxygen mixtures having different equivalence ratios. Digital photographs of the flames have been captured and the radial temperature profiles at different axial locations have been measured using a thermocouple. Numerical simulations have been carried out with a C2 chemical mechanism having 25 species and 121 reactions and with an optically thin radiation sub-model. The numerical results are validated against the experimental and numerical results for methane-air premixed flames reported in literature. Further, the numerical results are validated against the results from the present methane-oxygen flame experiments. Visible regions in digital flame photographs have been compared with OH isopleths predicted by the numerical model. Parametric studies have been carried out for a range of equivalence ratios, varying from 0.24 to 1.55. The contours of OH, temperature and mass fractions of product species such as CO, CO₂ and H₂O, are presented and discussed for various cases. By using the net methane consumption rate, an estimate of the laminar flame speed has been obtained as a function of equivalence ratio.     

Electronic structure and ordering of multilayers of Co and Ag on Cu(111) investigated by photoelectron spectroscopy

The growth and the electronic structure of multilayers of Co and Ag on Cu(111) at room temperature have been studied with photoelectron spectroscopy and low-energy electron diffraction (LEED). The coverage range spans from Co and Ag layers between one monolayer (ML) to stacking of several monolayers. Surface states and ordered structures have been identified at room temperature. A Ag-related surface state with a binding energy of 0.30 eV is identified in normal emission in the ultraviolet photoelectron spectra when silver constitutes the top layer. Core-level binding energy shifts of Ag 3d_5/2 reflect the changing surroundings of Ag. Hexagonal diffraction patterns are observed for sandwiches of consecutive layers of Co and Ag up to 5 layers. Since no interlayer diffusion is observed in the layer-by-layer formation of the films, multilayers of consecutive silver and cobalt on Cu(111) offer preparation of sandwiched magnetic–non-magnetic structures.     

Structure and propagation of two-dimensional,partially premixed,laminar flames in diesel engine conditions

We investigate the influence of inflow velocity (V_in) and scalar dissipation rate (χ) on the flame structure and stabilisation mechanism of steady, laminar partially premixed n-dodecane edge flames stabilised on a convective mixing layer. Numerical simulations were performed for three different χ profiles and several V_in (V_in = 0.2 to 2.5m/s). The ambient thermochemical conditions were the same as the Engine Combustion Network’s (ECN) Spray A flame, which in turn represents conditions in a typical heavy duty diesel engine. The results of a combustion mode analysis of the simulations indicate that the flame structure and stabilisation mechanism depend on V_in and χ. For low V_in the flame is attached. Increasing V_in causes the high-temperature chemistry (HTC) flame to lift-off, while the low-temperature chemistry (LTC) flame is still attached. A unique speed S_R associated with this transition is defined as the velocity at which the lifted height has the maximum sensitivity to changes in V_in. This transition velocity is negatively correlated with χ. Near $V_{in}=S_R$ a tetrabrachial flame structure is observed consisting of a triple flame, stabilised by flame propagation into the products of an upstream LTC branch. Further increasing the inlet velocity changes the flame structure to a pentabrachial one, where an additional HTC ignition branch is observed upstream of the triple flame and ignition begins to contribute to the flame stabilisation. At large V_in, the LTC is eventually lifted, and the speed at which this transition occurs is insensitive to χ. Further increasing V_in increases the contribution of ignition to flame stabilisation until the flame is completely ignition stabilised. Flow divergence caused by the LTC branch reduces the χ at the HTC branches making the HTC more resilient to χ. The results are discussed in the context of identification of possible stabilisation modes in turbulent flames.     

Photoionization mass spectrometry and modeling study of premixed flames of three unsaturated C5H8O2 esters

The detailed chemical structures of low-pressure premixed laminar flames fueled by three simple unsaturated C₅H₈O₂ esters, the methyl crotonate (MC), methyl methacrylate (MMA), and ethyl propenoate (EPE), are investigated using tunable synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry. Significant differences in the compositions of key reaction intermediates between these flames under similar flame conditions are observed. The results enable further refinement and validation of a detailed chemical kinetic reaction mechanism, which is largely based on a previous model for saturated esters. Detailed kinetic modeling describes how these differences are related to molecular structures, leading to unique fuel destruction pathways for each of these isomers. Meanwhile, the effect of carbon carbon double bonds on the combustion chemistry of small fatty acid esters is addressed.     

Electronic and magnetic properties of ultrathin films and interfaces investigated by dichroic core-level photoelectron spectroscopy

The electronic and magnetic structures of ultrathin films made of a ferromagnetic and a nonmagnetic material are theoretically investigated by means of magnetic dichroism in spin- and angle-resolved core-level photoelectron spectroscopy. How these properties manifest themselves in the photoemission intensities is analyzed with a focus on the interface between film and substrate. The dependence on both exchange and spin–orbit splitting, magnetic ordering, core-level shift and on the thickness of the covering layer are investigated in detail. Ultrathin films of Fe and Pd serve as prototypical systems because of their large exchange and spin–orbit splittings, respectively.     

Elucidation of surface structure and bonding by photoelectron spectroscopy?

Information obtained on the adsorption of small and medium-sized molecules (CO, O₂, CO₂, NO, C₂H₄, C₆H₆) at three metal surfaces (Mo, W, Ni) by X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS) is discussed in an attempt to establish what has been achieved, and what might be achieved in the elucidation of adsorption bonding at metal surfaces. Some of the individual results have been published by the present author with co-workers, and by other authors, but some results represent new work. Emphasis is placed on the detection of different states of adsorption, and then on interpretations of structure and bonding. The latter is divided into two areas, empirical interpretation by analogy between different adsorption systems, and in more absolute terms by consideration of the differences in electronic energy levels between the absorbate molecule in its gaseous and adsorbed state as well as differences between the metal levels in the clean and surface bonded state. Note is made of the problems of suitable reference levels and the phenomena of relaxation energies. Mo and W are taken as representative examples of adsorption confined usually to the monolayer regime; Ni is taken as an example of the situation where further reaction may occur. Most of the work described refers to polycrystalline films since little work has yet been done by XPS on adsorption at single crystal surfaces. A short general review of the quantitative aspects of XPS and UPS for analysis is given.     

Influence of ferrocene addition to a laminar premixed propene flame: Laser diagnostics, mass spectrometry and numerical simulations

The detailed influence of ferrocene in a low-pressure, fuel-rich, laminar, premixed propene/oxygen/argon flat flame was investigated experimentally using molecular beam sampling mass spectrometry (MBMS), laser-induced fluorescence (LIF), and compared to numerical simulations. MBMS was applied to analyze the species profiles of important intermediates in the flames with and without ferrocene doping. The concentration profile of iron atoms was measured with absorption sensitive LIF, which provides absolute number densities without additional calibrations. The flame temperature was obtained by two-line OH LIF measurements. One dimensional numerical simulations of the flames using detailed models from the literature were performed and the modeling results are compared with the experimental measurements. The iron measurements show reasonable agreement with the numerical simulation, while some discrepancies were found at larger heights. The MBMS measurements show a decrease in flame velocity when ferrocene was added, which was not provided by the model.     

Electronic structure of carbyne studied by X-ray photoelectron spectroscopy and X-ray emission spectroscopy

The electronic structure of amorphous carbyne has been investigated by X-ray photoelectron spectroscopy and X-ray emission spectroscopy. Carbyne band structure has been calculated semiempirically and the experimental data have been interpreted on the basis of the calculation results. The valence band width was found to be about 20 eV which is the same as that in all other condensed carbon structures. The fine satellite structure near the 1s line of carbon has been studied. It is shown that the energy bands in carbyne are arranged in a mirror-like way relative to the Fermi level. The real carbyne structure is susceptible to conformations which affect primarily the π-subband structure.     

Elementary relaxation processes investigated by femtosecond photoelectron spectroscopy of two‐dimensional materials

Elementary scattering processes in solid matter occur on ultrafast timescales and photoelectron spectroscopy in the time domain represents an excellent tool for their analysis. Conventional photoemission accesses binding energies of electronic states and their momentum dispersion. The use of femtosecond laser pulses in pump‐probe experiments allows obtaining direct insights to the energy and momentum dependence of ultrafast dynamics. This article introduces the elementary interaction processes and emphasizes recent work performed in this rapidly developing field. Decay processes in the low excitation limit are addressed, where electrons decay according to their interaction with carriers in equilibrium. Here, hot electron relaxation in epitaxial metallic film is reviewed. In the limit of an intense optical excitation, scattering of the excited electrons among each other establishes a non‐equilibrium state. Results on charge‐density wave materials and the effect of coherent nuclear motion on the electronic structure, which can break low symmetry ground states, are discussed. Figure reprinted with permission from [71].     

Laser multiphoton and multistep photoionization of molecules and mass spectrometry

A review of laser-induced photoionization of polyatomic molecules and the application of this process in mass-spectrometry is presented. Combination of laser selective photoionization and mass spectral analysis of fragments as a promising tool for the detection of trace amounts of complex molecules is considered particularly.     

Dynamic secondary ion mass spectrometry and X-ray photoelectron spectroscopy on artistic bronze and copper artificial patinas

To prevent the natural processes of decay and to develop and improve the treatments of conservation and restoration of artistic bronzes meaning statues and sculptures, it is important understanding the patination processes and the knowledge of artificially corroded surfaces. Chemical and physical characterization of artificial patinas obtained on artistic bronzes and coppers by using the 19th century Western traditional patination techniques and recipes by means of SEM-EDS, light microscopy and ATR/FT-IR has been done in previous studies [I.Z. Balta, L. Robbiola, Characterization of artificial black patinas on artistic cast bronze and pure copper by using SEM-EDS and light microscopy, in: Proceedings of the 13th European Microscopy Congress, 22-27 August 2004, Antwerp, Belgium, EMC 2004 CD-Rom Conference Preprints; I.Z. Balta, L. Robbiola, Traditional artificial artistic bronze and copper patinas—an investigation by SEM-EDS and ATR/FT-IR, in: Proceedings of the 8th International Conference on Non Destructive Investigations and Microanalysis for the Diagnostics and Conservation of the Cultural and Environmental Heritage, 15-19 May 2005, Lecce, Italy, ART’05 CD-Rom Conference Preprints]. Differences in morphology (structure, thickness, porosity, adherence, compactity, uniformity, homogeneity) and also in composition, on both artistic cast bronze and pure copper patinas, were clearly evidenced. Further in-depth investigation is required to be carried out in order to better understand the patinas mechanisms of formation and the layers kinetics of growth. The elemental and chemical analysis, either on a surface monolayer or in a depth profile, by using the Secondary Ion Mass Spectrometry (SIMS) and X-ray Photoelectron Spectroscopy (XPS) techniques, can provide this kind of information, unique at trace-level sensitivity. SIMS has proved to be a suitable analytical technique for analyzing small amounts of material with high atomic sensitivity (ppm or even ppb) and high depth/lateral resolution in the micron and sub-micron range [R.G. Wilson, F.A. Stevie, C.W. Magee, Secondary Ion Mass Spectrometry: A Practical Handbook for Depth Profiling and Bulk Impurity Analysis, Wiley & Sons, New York, 1989; M. Dowsett, A. Adriaens, The role of SIMS in cultural heritage studies, Nucl. Instr. Meth. Phys. Res. B 226 (2004) 38-52]. XPS has the ability to provide detailed chemical information on virtually each kind of solid sample, and elemental identification is therefore possible due to the core level photoemission. The most important advantage is the high surface sensitivity of the chemical information (a few monolayers) [E. Ciliberto, G. Spoto, Modern Analytical Methods in Art and Archaeology, John Wiley & Sons, Inc., New York, 2000]. In addition elements’ relative abundance can be made semi-quantitative or quantitative and information on chemical bonds can be derived.The aim of the present work is to highlight the advantages and the limits of XPS and Dynamic SIMS surface analytical techniques for the characterization of artistic bronze and copper artificial patinas. The results obtained on the analyzed samples allowed the distribution of the main elements in the corrosion patinas layers and the contribution of each elements present in bronze matrix to the color of the resulting patinas to be precisely revealed. This information could be used for comparative studies between artificial and natural patinas, and also for provenience and authentication studies for artistic and archaeological bronzes.     

Probing fuel-specific reaction intermediates from laminar premixed flames fueled by two C5 ketones and model interpretations

The flame chemistry was explored for two C₅ ketones with distinct structural features, cyclopentanone (CPO) and diethyl ketone (DEK). Quantitative information for numerous species, including some reactive intermediates, was probed from fuel-rich (?= 1.5) laminar premixed flames fueled by the ketones with a photoionization molecular-beam mass spectrometer (PI-MBMS). Furthermore, a new kinetic model was proposed aimed at interpreting the high-temperature combustion chemistry for both ketones, which could satisfactorily predict the current flame speciation measurements. Experimental observations in combination with modeling analyses were used to reveal the similarities and differences between the compositions of the species pools of the two flames, with emphasis on the effects of the carbonyl functionality on pollutants formations. Besides some primary species which preserve fuel-specific features produced from initial steps of fuel consumptions, basic C₁C₄ intermediates also differ much between the two flames. More abundant intermediates were observed in the CPO flame because the cyclic fuel structure enables ring-opening processes followed by formations of C₃ and C₄ hydrocarbons which cannot be easily produced from the two isolated ethyl moieties in DEK under flame conditions. The consumptions of C₃C₄ hydrocarbons in the CPO flame further lead to larger C₅C₆ species which were under the detection limit in the DEK flame. In both flames, the tightly bonded carbonyl groups in the fuels tend to be preserved, leading to carbon monoxide through α-scissions of fuel-related acyl radicals. The carbonyl moieties in most detected C₁C₃ aldehydes and ketones form through oxidations of hydrocarbon species rather than directly originating from the fuels.     

The electronic structure of KMnO4 investigated by photoemission and electron-energy-loss spectroscopy

From photoemission and electron-energy-loss data the following picture of KMnO₄, with Mn^VII (with a formal charge state Mn⁷⁺ (3d ⁰)) tetrahedrally surrounded by four O^2–-ions, is deduced: strong covalent bonding between Mn^VII and O^2– leads to a considerable occupation of the Mn-3 d shell. The ground state of the (MnO₄)^–1 molecule is an orbital and spin singlet as seen by the absence of any multiplet splitting in the Mn core levels. The valence band shows a four peak structure extending form 4 eV to 8 eV below the Fermi energy. The first peak at 4.2 eV has mainly O-2p character. The remaining peaks are of strongly mixed Mn-3d/O-2p character due to the covalent bonding. This mixing decreases with increasing binding energy. The electron energy loss data show a variety of structures between 2 eV and 10 eV independent of the primary electron energy which defines them as dipole allowed charge-transfer transitions. An additional excitation at 1.8 eV decreases quickly in intensity with increasing electron energy which classifies it as a dipole or spin forbidden transition in the compound. This energy is close to the value of 1.6 eV reported for the activation energy observed in electrical transport data. The results are compared to quantum chemical molecular orbital calculations of the (MnO₄)^–1 molecule.Physics Department, Allahabad University Allahabad 211002, India     

The interaction between vapor-deposited Al atoms and methylester-terminated self-assembled monolayers studied by time-of-flight secondary ion mass spectrometry,X-ray photoelectron spectroscopy and infrared reflectance spectroscopy

The deposition of 2 Å of Al metal onto a monolayer of methylester-terminated alkanethiolate (HS(CH₂)₁₅CO₂CH₃) self-assembled on polycrystalline Au(111) was studied using time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS) and infrared reflectance spectroscopy (IRS). The deposited Al was found to be highly reactive with the oxygen atoms in the self-assembled monolayer terminal functional group. No reactivity between Al and the methylene backbone of the monolayer was observed, nor was any Al observed at the monolayer/Au interface. However, the deposition of Al does induce some chain disordering.     

Synthesis of platinum metalloporphyrins and investigation of their electronic structure by photoelectron spectroscopy

Features of the electronic structure of the valence band and Pt4f, Pt4d, C1s, O1s, and N1s core levels of the tetraphenylporphyrin (TPP) and synthesized Pt-TPP(p-COOCH₃)₄, Pt-TPP(m-OCH₃)₄, and PtCl₂-TPP(m-OCH₃)₄ platinum metalloporphyrins are investigated by photoelectron spectroscopy.