On the Schlafli differential formula based on edge lengths of tetrahedron in <Emphasis Type="Italic">H</Emphasis><Superscript>3</Superscript> and <Emphasis Type="Italic">S</Emphasis><Superscript>3</Superscript>

We obtain a new version of Schlafli differential formula based on edge lengths for the volume of a tetrahedron in hyperbolic and spherical 3-spaces, by using the edge matrix of a hyperbolic(or spherical) tetrahedron and its submatrix.      

Heat flux measurements in stagnation point methane/air flames with thermographic phosphors

Light-induced phosphorescence from thermographic phosphors was used to study the wall temperatures and heat fluxes from nearly one-dimensional flat premixed flames. The investigated flames were stoichiometric, lean and rich laminar methane/air flames with equivalence ratios of φ = 1, φ = 0.75 and φ = 1.25 at ambient pressure. The flames were burning in a stagnation point arrangement against a water-cooled plate. The central part of this plate was an alumina ceramic plate coated from both sides with chromium-doped alumina (ruby) and excited with a Nd:YAG laser or a green light-emitting diode (LED) array to measure the wall temperature from both sides and thus the heat flux rate from the flame. The outlet velocity of the gases was varied from 0.1 to 1.2 m/s. The burner to plate distance (H) ranged from 0.5 to 2 times the burner exit diameter (d = 30 mm). The measured heat flux rates indicate the change of the flame stabilization mechanism from a burner stabilized to a stagnation plate stabilized flame. The results were compared to modeling results of a one-dimensional stagnation point flow, with a detailed reaction mechanism. In order to prove the model, gas phase temperatures were measured by OH-LIF for a stoichiometric stagnation point flame. It turns out that the flame stabilization mechanism and with it the heat fluxes change from low to high mass fluxes. This geometry may be well suited for further studies of the elementary flame wall interaction.     

Metabolic infrastructure of pregnant women with methylenetetrahydrofolate reductase polymorphisms: A metabolomic analysis

The aim of this study was to demonstrate the altered metabolic infrastructure of pregnant women with methylenetetrahydrofolate reductase (MTHFR) polymorphisms at first trimester and during delivery. Eight singleton pregnant women with MTHFR polymorphisms were compared with 10 normal pregnant women. Maternal blood samples were obtained twice during their pregnancy period (between the 11th and 14th gestational weeks and during delivery). Metabolomic analysis was performed using GC–MS. The GC–MS based metabolomic profile helped identify 95 metabolites in the plasma samples. In the MTHFR group, the levels of 1-monohexadecanoylglycerol, pyrophosphate, benzoin, and linoleic acid significantly decreased (P ˂ 0.05 for all), whereas the levels of glyceric acid, l -tryptophan, l -alanine, l -proline, norvaline, l -threonine, and myo-inositol significantly increased (P ˂ 0.01 for the first two metabolites, P ˂ 0.05 for the others) at 11–14 gestational weeks. Conversely, the levels of benzoin, 1-monohexadecanoylglycerol, pyruvic acid, l -proline, phosphoric acid, epsilon-caprolactam, and pipecolic acid significantly decreased in the MTHFR group, whereas metabolites such as hexadecanoic acid and 2-hydroxybutyric acid increased significantly in the study group during delivery. An impaired energy metabolism pathway, vitamin B complex disorders, tendency for metabolic acidosis (oxidative stress), and the need for cell/tissue support seem prevalent in pregnancies with MTHFR polymorphisms.     

The influence of pressure and equivalence ratio on the NTC behavior of methane

Methane based polygeneration processes in piston engines offer the possibility of a controllable and flexible conversion of energy, to up-convert low value chemicals and to store energy. These processes preferably take place under fuel-rich conditions and at high pressures. Under fuel-rich conditions, there was one experimental report that a distinctive negative temperature coefficient (NTC) behavior occurs in methane oxidation (Petersen et al., 1999). To design a polygeneration process, reliable kinetic models are required to capture the impact of pressure and equivalence ratio variations on reactivity of the gas mixtures. Here, the experimental basis for methane oxidation is expanded to high pressures and very fuel-rich conditions and compared to literature models, both with special emphasis on the NTC behavior. The oxidation of methane/oxygen mixtures at 2 ≤ Φ≤ 20 and pressures ranging from 1 to 20 bar is investigated. The literature reaction mechanisms are assessed with respect to their ability to predict this phenomenon and used to identify reaction pathways. It is found that NTC behavior occurs in a temperature range between 700 and 1000 K and at pressures higher than 5 bar. The lower temperature limit is slightly shifted towards higher temperatures with decreasing equivalence ratio. In addition, the higher the equivalence ratio, the broader the pressure range, in which the NTC behavior is observed. In general, predictions of some models are in good agreement with the experimental data. Reaction path analyses reveal that the competition between oxidation and recombination pathways are responsible for the NTC region in methane oxidation.     

Phosphorescence properties of sol–gel derived ruby measured as functions of temperature and Cr<Superscript>3+</Superscript> content

A novel approach for the contactless measurement of surface temperatures is to evaluate the temperature dependent phosphorescence properties of chromium doped aluminium oxide (ruby) coatings, such as phosphorescence intensity, spectral distribution, or the phosphorescence lifetime. However, these properties are also affected by the chromium content in the films. In the present study the phosphorescence lifetimes were studied for the first time as a function of the chromium content. We use a simple sol–gel depositing technique for the preparation of precisely doped ruby coatings in Si(100) substrates. These coatings (Cr-to-Al-ratios y between 0% and 6.8 at. %) are well suited for studying the influence of the chromium concentration on the phosphorescence properties: at room temperature (294 K), the phosphorescence intensity is strongly affected by the chromium doping (maximum at y∼1–1.5%) while the spectrum shifts only slightly with varying chromium content. The phosphorescence lifetime τ at 294 K remains constant with varying Cr³⁺ content below y∼1.1%, and decreases strongly above y∼1.1%. Thus, ruby doped with y∼1% seems to be most promising as a temperature sensor because it shows the highest phosphorescence intensity and a low variance in the phosphorescence lifetimes. Due to the latter property the temperature evaluation from τ is less affected by imprecise doping. The phosphorescence lifetimes of several sol–gel ruby coatings (y=1.1%) on Si(100) substrates were measured as a function of the temperature to be between 2.7 ms at 294 K and 4 μs at 833 K. PACS 07.20.Dt; 78.55.-m; 78.66.-w     

Temperature measurement in fuel-rich non-sooting low-pressure hydrocarbon flames

Several temperature measurement techniques were compared for the investigation of fuel-rich, premixed, flat, low-pressure flames of propene, acetylene, and cyclopentene with maximum temperatures around 2400 K. Vibrational Stokes/anti-Stokes Raman measurements with a KrF excimer laser using CO, H₂, and H₂O as temperature indicators were examined at 50 and 200 mbar for different flame stoichiometries. Also, laser-induced fluorescence (LIF) of OH in the A-X band was used, and complementary lifetime measurements were performed to account for a variation of fluorescence quantum yield with rotational quantum number. LIF using seeded NO (0.2-1.0%) was applied both in point-wise and 1D temperature measurement in spite of the anticipated interaction of NO with the fuel-rich flame chemistry. Furthermore, thermocouple measurements were performed in the preheat zone. These techniques were compared with respect to accuracy and the potential for routine applications under fuel-rich low-pressure conditions.