Investigation of hydrogen-air ignition sensitized by nitric oxide and by nitrogen dioxide

The sensitization of stoichiometric hydrogen-air ignition by NO, NO2 and a mixture of NO and NO2 was investigated behind reflected shock waves in a shock tube. Induction times were measured in pressure range 0.27 to 2.0 atm, temperature range 800 to 1500 K, and for NO or NO2 mole percent between 0.0 and 4.5. Addition of both NO and NO2 reduced the measured induction times. The experimental data are interpreted in terms of H2-O2-NO(x) oxidation reaction mechanisms. The influence of NO(x) upon a supersonic combustion ramjet combustor test, conducted in an arc-heated facility, is assessed

Combined surface science and density functional theory approach towards water ordered structures formation on magnetite

Three different adsorbed water species were distinguished on Fe-terminated Fe3O4 multilayer films using thermal desorption spectroscopy (TDS), and ultraviolet photoelectron spectroscopy (UPS) measured under adsorption-desorption equilibrium conditions [1]. By means of density functional theory (DFT) calculations, the first species (-water) were confirmed to correspond to dissociative water adsorption with the resulting hydroxyl (OH) groups of water on the surface iron (Fe) sites, and the hydrogen (H) atoms adsorbed onto surface oxygen (O) sites. The DFT results for the -water structure are consistent with the two OH-stretch lines observed by infrared-reflection-absorption-spectroscopy (IRAS) [2], and the UPS study [1]. The DFT calculations confirm the subsequent formation of dimeric water structures (-water) formed by H-bonded molecular water to the surface OH-groups on surface-Fe, and the H on the surface-O sites, respectively, as suggested by IRAS [2] and low energy electron diffraction (LEED) experiments [1]. The DFT results reveal that formation of the -water overlayer structure results from the diffusion of the mobile H-atoms from the initially molecular adsorbed water molecules on iron sites followed by formation of a transition structure with the H-atom adsorbed on nearest-neighboring oxygen sites, diffusing over the surface to adsorb on-top onto the next O-sites. This result is consistent with the proposed second-order kinetics of the recombinative adsorption process [1]. 1. Y. Joseph et. al., J. Phys. Chem. B 104, 3224 (2000). 2. U. Leist et al., Phys. Chem. Chem. Phys. 5, 2435 (2003)

Surface structure and water adsorption on Fe₃O₄(111): Spin-density functional theory and on-site Coulomb interactions

The surface structure of magnetite Fe3O4(111) in contact with oxygen and water is investigated using spin density functional theory plus on-site Coulomb interactions. The present results unravels apparent contradictions in the experimental data regarding the equilibrium stoichiometry of the bare surface termination. Both for 298 K and 1200 K, the equilibrium structure is terminated by 1/4 monolayer (ML) of iron (Fe) on top of a full oxygen layer, consistent with an earlier low-energy electron diffraction analysis. Nontheless, the calculated negative slope of the surface energies vs oxygen partial pressure shows that a 1/2 ML Fe termination would become stable under oxygen poor conditions at high temperatures, in agreement to interpretation of scanning tunneling microscopy experiments. Initial water adsorption is dissociative and saturates when all Fe sites are occupied by OH groups while the H atoms bind to surface oxygen. Further water bridges the OH and H groups resulting in a quite unique type of H-bonded molecular water with its oxygen forming a hydronium ion like structure OH3+-OH. This water structure is different from the water dimeric structures found as yet on oxide and metal surfaces for partially dissociated (H2O-OH-H) overlayers

Numerical simulations challenged on the prediction of massive subhalo abundance in galaxy clusters: the case of Abell 2142

In this Letter we compare the abundance of member galaxies of a rich, nearby ($z=0.09$) galaxy cluster, Abell 2142, with that of halos of comparable virial mass extracted from sets of state-of-the-art numerical simulations, both collisionless at different resolutions and with the inclusion of baryonic physics in the form of cooling, star formation, and feedback by active galactic nuclei. We also use two semi-analytical models to account for the presence of orphan galaxies. The photometric and spectroscopic information, taken from the Sloan Digital Sky Survey Data Release 12 (SDSS DR12) database, allows us to estimate the stellar velocity dispersion of member galaxies of Abell 2142. This quantity is used as proxy for the total mass of secure cluster members and is properly compared with that of subhalos in simulations. We find that simulated halos have a statistically significant ($\gtrsim 7$ sigma confidence level) smaller amount of massive (circular velocity above $200\,{\rm km\, s^{-1}}$) subhalos, even before accounting for the possible incompleteness of observations. These results corroborate the findings from a recent strong lensing study of the Hubble Frontier Fields galaxy cluster MACS J0416 \citep{grillo2015} and suggest that the observed difference is already present at the level of dark matter (DM) subhalos and is not solved by introducing baryonic physics. A deeper understanding of this discrepancy between observations and simulations will provide valuable insights into the impact of the physical properties of DM particles and the effect of baryons on the formation and evolution of cosmological structures.Comment: 8 pages, 2 figures. Modified to match the version published in ApJ

Structure and spacing of cellulose microfibrils in woody cell walls of dicots

The structure of cellulose microfibrils in situ in wood from the dicotyledonous (hardwood) species cherry and birch, and the vascular tissue from sunflower stems, was examined by wide-angle X-ray and neutron scattering (WAXS and WANS) and small-angle neutron scattering (SANS). Deuteration of accessible cellulose chains followed by WANS showed that these chains were packed at similar spacings to crystalline cellulose, consistent with their inclusion in the microfibril dimensions and with a location at the surface of the microfibrils. Using the Scherrer equation and correcting for considerable lateral disorder, the microfibril dimensions of cherry, birch and sunflower microfibrils perpendicular to the [200] crystal plane were estimated as 3.0, 3.4 and 3.3 nm respectively. The lateral dimensions in other directions were more difficult to correct for disorder but appeared to be 3 nm or less. However for cherry and sunflower, the microfibril spacing estimated by SANS was about 4 nm and was insensitive to the presence of moisture. If the microfibril width was 3 nm as estimated by WAXS, the SANS spacing suggests that a non-cellulosic polymer segment might in places separate the aggregated cellulose microfibrils

FLIGHT CONTROL RESEARCH LABORATORY UNMANNED AERIAL SYSTEM WIND SHEAR ON-LINE IDENTIFICATION

An algorithm to perform the on line identification of the wind shear components suitable for the UAS characteristics has been implemented. The mathematical model of aircraft and wind shear in the augmented state space has been built without any restrictive assumption on the dynamic of wind shear. Because of the strong velocity variations typical of wind shear induce severe accelerations on the aircraft the wind shear effects have been modeled as external forces and moments applied on the aircraft. The identification problem addressed in this work has been solved by using the Filter error method approach. An Extended Kalman Filter has been developed to propagate state. It has been tuned by using a database of measurements through off-line identification of the process noise covariance matrix. Afterwards the implemented EKF has been employed to estimate onboard either aircraft state or turbulence, with significant savings in terms of time and computing resources. Robustness of implemented algorithm has been verified by means of several tests. The obtained results show the feasibility of the tuned up algorithm. In fact it is possible, by using a few numbers of low cost sensors, to estimate with a noticeable accuracy the augmented state vector. Besides a very short computation time is required to performthe augmented state estimation even by using low computation power