IR laser absorption diagnostic for C2H4 in shock tube kinetics studies

An IR laser absorption diagnostic has been further developed for accurate and sensitive time‐resolved measurements of ethylene in shock tube kinetic experiments. The diagnostic utilizes the P14 line of a tunable CO₂ gas laser at 10.532 μm (the (0 0 1) → (1 0 0) vibrational band) and achieves improved signal‐to‐noise ratio by using IR photovoltaic detectors and accurate identification of the P14 line via an MIR wavemeter. Ethylene absorption cross sections were measured over 643–1959 K and 0.3–18.6 atm behind both incident and reflected shock waves, showing evident exponential decay with temperature. Very weak pressure dependence was observed over the pressure range of 1.2–18.6 atm. By measuring ethylene decomposition time histories at high‐temperature conditions (1519–1895 K, 2.0–2.8 atm) behind reflected shocks, the rate coefficient of the dominant elementary reaction C₂H₄ + M → C₂H₂ + H₂ + M was determined to be k₁ = (2.6 ± 0.5) × 10¹⁶exp(?34,130/T, K) cm³ mol^?1 s^?1 with low data scatter. Ethylene concentration time histories were also measured during the oxidation of 0.5% C₂H₄/O₂/Ar mixtures varying in equivalence ratio from 0.25 to 2. Initial reflected shock conditions ranged from 1267 to 1440 K and 2.95 to 3.45 atm. The measured time histories were compared to the modeled predictions of four ethylene oxidation mechanisms, showing excellent agreement with the Ranzi et al. mechanism (updated in 2011). This diagnostic scheme provides a promising tool for the study and validation of detailed hydrocarbon pyrolysis and oxidation mechanisms of fuel surrogates and realistic fuels. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 423–432, 2012     

Aerodynamic optimization of the flat-plate leading edge for experimental studies of laminar and transitional boundary layers

This work is concerned with the design of a leading edge for a flat-plate model used to study laminar and transitional boundary layers. For this study, the flow over the complete boundary-layer model, including leading edge, flat section, and trailing-edge flap, is modeled. The effect of important geometrical features of the leading edge on the resulting pressure distribution, starting from the well-known symmetric modified super ellipse, is investigated. A minimal pressure gradient on the measurement side of the plate is achieved using an asymmetrical configuration of modified super ellipses, with a thickness ratio of 7/24. An aerodynamic shape optimization is performed to obtain a novel leading edge shape that greatly reduces the length of the non-zero pressure gradient region and the adverse pressure gradient region compared to geometries defined by ellipses. Wind tunnel testing is used to validate the numerical solutions.     

Regular Binary Thermal Lattice-Gases

We analyze the power spectrum of a regular binary thermal lattice gas in two dimensions and derive a Landau–Placzek formula, describing the power spectrum in the long-wavelength, low frequency domain, for both the full mixture and a single component in the binary mixture. The theoretical results are compared with simulations performed on this model and show a perfect agreement. The power spectrums are found to be similar in structure as the ones obtained for the continuous theory, in which the central peak is a complicated superposition of entropy and concentration contributions, due to the coupling of the fluctuations in these quantities. Spectra based on the relative difference between both components have in general additional Brillouin peaks as a consequence of the equipartition failure.     

Strain rate change tests with the Split Hopkinson Bar method

In this paper, methods to produce rapid strain rate changes for strain rate sensitivity measurements in Split Hopkinson Bar arrangements are presented and discussed. Two different cases are considered: a strain rate change test within the high strain rate region in compression, and a tension test incorporating a large strain rate jump directly from the low strain rate region to high strain rates. The former method is based on the loading wave amplitude manipulation, while the latter method is based on the incorporation of a low strain rate loading device into a Tensile Split Hopkinson Bar apparatus.     

Generation of low-timing-jitter femtosecond pulse trains with 2 GHz repetition rate via external repetition rate multiplication

Generation of low-timing-jitter 150 fs pulse trains at 1560 nm with 2 GHz repetition rate is demonstrated by locking a 200 MHz fundamental polarization additive-pulse mode-locked erbium fiber laser to high-finesse external Fabry-Perot cavities. The timing jitter and relative intensity noise of the repetition-rate multiplied pulse train are investigated.     

Intermediate-temperature polymorphic phase transition in KH2PO4: A synchrotron X-ray diffraction study

We have used synchrotron X-ray diffraction to investigate the structural and chemical changes undergone by polycrystalline KH₂PO₄ (KDP) upon heating within the 30-250 °C temperature interval. Our data show evidence of a polymorphic transition at T∼190 °C from the room-temperature tetragonal KDP phase to a new intermediate-temperature monoclinic KDP modification (spacegroup P2₁/m and lattice parameters a=7.590, b=6.209, c=4.530 Å, and β=107.36°). The monoclinic RDP polymorph remains stable upon further heating to 235 °C, and is isomorphic to its RbH₂PO₄ and CsH₂PO₄ counterparts.     

The effect of signal duration on the underwater detection thresholds of a harbor porpoise (Phocoena phocoena) for single frequency-modulated tonal signals between 0.25 and 160 kHz

The underwater hearing sensitivity of a young male harbor porpoise for tonal signals of various signal durations was quantified by using a behavioral psychophysical technique. The animal was trained to respond only when it detected an acoustic signal. Fifty percent detection thresholds were obtained for tonal signals (15 frequencies between 0.25-160 kHz, durations 0.5-5000 ms depending on the frequency; 134 frequency-duration combinations in total). Detection thresholds were quantified by varying signal amplitude by the 1-up 1-down staircase method. The hearing thresholds increased when the signal duration fell below the time constant of integration. The time constants, derived from an exponential model of integration [Plomp and Bouman, J. Acoust. Soc. Am. 31, 749-758 (1959)], varied from 629 ms at 2 kHz to 39 ms at 64 kHz. The integration times of the porpoises were similar to those of other mammals including humans, even though the porpoise is a marine mammal and a hearing specialist. The results enable more accurate estimations of the distances at which porpoises can detect short-duration environmental tonal signals. The audiogram thresholds presented by Kastelein et al. [J. Acoust. Soc. Am. 112, 334-344 (2002)], after correction for the frequency bandwidth of the FM signals, are similar to the results of the present study for signals of 1500 ms duration. Harbor porpoise hearing is more sensitive between 2 and 10 kHz, and less sensitive above 10 kHz, than formerly believed.     

Fluorescence monitoring of microchip capillary electrophoresis separation with monolithically integrated waveguides

Using femtosecond laser writing, optical waveguides were monolithically integrated into a commercial microfluidic lab-on-a-chip device, with the waveguides intersecting a microfluidic channel. Continuous-wave laser excitation through these optical waveguides confines the excitation window to a width of 12 microm, enabling high-resolution monitoring of the passage of different types of fluorescent analytes when migrating and being separated in the microfluidic channel by microchip capillary electrophoresis. Furthermore, we demonstrate on-chip-integrated waveguide excitation and detection of a biologically relevant species, fluorescently labeled DNA molecules, during microchip capillary electrophoresis. Well-controlled plug formation as required for on-chip integrated capillary electrophoresis separation of DNA molecules, and the combination of waveguide excitation and a low limit of detection, will enable monitoring of extremely small quantities with high spatial resolution.     

Determination of a double Lie groupoid by its core diagram

In a double groupoid S, we show that there is a canonical groupoid structure on the set of those squares of S for which the two source edges are identities; we call this the core groupoid of S. The target maps from the core groupoid to the groupoids of horizontal and vertical edges of S are now base-preserving morphisms whose kernels commute, and we call the diagram consisting of the core groupoid and these two morphisms the core diagram of S. If S is a double Lie groupoid, and each groupoid structure on S satisfies a natural double form of local triviality, we show that the core diagram determines S and, conversely, that a locally trivial double Lie groupoid may be constructed from an abstractly given core diagram satisfying some natural additional conditions.

In the algebraic case, the corresponding result includes the known equivalences between crossed modules, special double groupoids with special connection (Brown and Spencer), and cat¹-groups (Loday). These cases correspond to core diagrams for which both target morphisms are (compatibly) split surjections.