The vacuum uv emission spectrum of the 15N22+ molecular ion

The vacuum uv emission of the ¹⁵N₂²⁺ ion has been recorded for the first time. Rotational analysis of two bands, analogous to those already observed in the case of the natural isotope, confirm their assignment to the D¹Σ_u⁺-X¹Σ_g⁺ (0, 0) and (1, 1) bands. More precise data are also obtained for the ³Σ_g^? state which perturbs ground state vibrational levels.     

Travelling wave mathematical analysis and efficient numerical resolution for a one-dimensional model of solid propellant combustion

We investigate a model of solid propellant combustion involving surface pyrolysis coupled to finite activation energy gas-phase combustion. Existence and uniqueness of a travelling wave solution are established by extending dynamical system tools classically used for premixed flames, dealing with the additional difficulty arising from the surface regression and pyrolysis. An efficient shooting method allows to solve the problem in phase space without resorting to space discretisation nor fixed-point Newton iterations. The results are compared to solutions from a CFD code developed at ONERA, assessing the efficiency and potential of the method, and the impact of the modelling assumptions is evaluated through parametric studies.     

Polarized light and X-ray precession study of the ferroelastic domains of YBa2Cu3O7-δ

The ferroelastic domains of the orthorhombic phase of YBa₂Cu₃O_7- have been observed in polarized light on ceramics and single crystals. By combining polarized light microscopy with the X-ray precession technique, the correlation of the orientation of the orthorhombica- andb-axes with that of thea-b-plane bireflectance, reflection dichroism, transmission dichroism (at a thickness of about 1m), reflection tints generated with compensators and upon uncrossing of polars, as well as the orientation of etch pits has been realized on ferroelastic single domains, bi-domains and more complicated domain patterns. Four ferroelastic orthorhombic domain states have been identified, at variance with former group theoretical considerations, predicting only two states. Ensembles of lamellar domains beyond optical resolution generate strong bireflectance with principal axes rotated by 45° relative to the truea, b-directions.     

Exact partition functions and correlation functions of multiple Hamiltonian walks on the Manhattan lattice

This is a general and exact study of multiple Hamiltonian walks (HAW) filling the two-dimensional (2D) Manhattan lattice. We generalize the original exact solution for a single HAW by Kasteleyn to a system ofmultiple closed walks, aimed at modeling a polymer melt. In 2D, two basic nonequivalent topological situations are distinguished. (1) the Hamiltonian loops are allrooted andcontractible to a point:adjacent one to another, and, on a torus,homotopic to zero. (2) the loops can encircle one another and, on a torus, canwind around it. Forcase 1, the grand canonical partition function and multiple correlation functions are calculated exactly as those of multiple rooted spanningtrees or of a massive 2Dfree field, critical at zero mass (zero fugacity). The conformally invariant continuum limit on a Manhattantorus is studied in detail. The melt entropy is calculated exactly. We also consider the relevant effect of free boundary conditions. The number of single HAWs on Manhattan lattices with other perimeter shapes (rectangular, Kagomé, triangular, and arbitrary) is studied and related to the spectral theory of the Dirichlet Laplacian. This allows the calculation of exact shape-dependent configuration exponents y. An exact surface critical exponent is obtained. Forcase 2, nested and winding Hamiltonian circuits are allowed. An exact equivalence to thecritical Q-state Potts model exists, whereQ ^1/2 is the walk fugacity. The Hamiltonian system is then always critical (forQ<-4). The exact critical exponents, in infinite numbers, are universal and identical to those of theO(n=Q ^1/2) model in its low-temperature phase, i.e. are those of dense polymers. The exact critical partition functions on the torus are given from conformai invariance theory. These models 1 and 2 yield the two first exactly solved models of polymer melts.     

Search for universal extra dimensions in pp collisions

We present a search for Kaluza-Klein (KK) particles predicted by models with universal extra dimensions (UED) using a data set corresponding to an integrated luminosity of 7.3 fb(-1), collected by the D0 detector at a pp center-of-mass energy of 1.96 TeV. The decay chain of KK particles can lead to a final state with two muons of the same charge. This signature is used to set a lower limit on the compactification scale of R(-1)>260 GeV in a minimal UED model.     

Measurements of WW and WZ production in W + jets final states in pp collisions

We study WW and WZ production with ?νqq (?=e,μ) final states using data collected by the D0 detector at the Fermilab Tevatron Collider corresponding to 4.3 fb(-1) of integrated luminosity from pp collisions at sqrt[s]=1.96 TeV. Assuming the ratio between the production cross sections σ(WW) and σ(WZ) as predicted by the standard model, we measure the total WV (V=W,Z) cross section to be σ(WV)=19.6(-3.0)(+3.2) pb and reject the background-only hypothesis at a level of 7.9 standard deviations. We also use b-jet discrimination to separate the WZ component from the dominant WW component. Simultaneously fitting WW and WZ contributions, we measure σ(WW)=15.9(-3.2)(+3.7) pb and σ(WZ)=3.3(-3.3)(+4.1) pb, which is consistent with the standard model predictions.     

Esr Studies of Some Crowded Free Radicals Derived from Oxalate Esters

The temperature independent esr spectrum of di-i-Propyl-t-butylmethyl radical, derived from photolysis of oxalate ester, indicates a frozen “cogwhell” conformation for this specie. The neo-pentyl substituted oxalate esters are suggested to qive β-hydrogen abstraction on presence of di-t-butylperoxide on photolysis.     

Study of phase transition in a [CdHgI4 : 0.2AgI] mixed conducting composite system doped with KI and K2SO4

New composite superionic systems, [CdHgI₄?:?0.2AgI]?:?0.xKI and [CdHgI₄?:?0.2AgI]?:?0.xK₂SO₄ (x?=?0.2, 0.4, 0.6?mol. wt%), were prepared, using [CdHgI₄?:?0.2AgI] mixed composite system as the host. Electrical conductivity was measured to study the transition behavior at frequencies of 100?Hz, 120?Hz, 1?kHz, and 10?kHz in the temperature range from 150°C to 250°C using a GENRAD 1659 RLC Digibridge. A sharp increase in conductivity was observed during β?→?α phase transition. Upon increasing the dopant-to-host ratio, the conductivity of the superionic systems exhibited Arrhenius (thermally activated)-type behavior. Differential thermal analysis, differential scanning calorimetry, thermogravimetric analysis, and X-ray powder diffraction were performed to confirm the doping effect and transition in the host. The phase transition temperature increased with an increase in the dopant concentration. Activation energies in eV for pre- and post-transition phase behavior are reported.     

Experimental study of a confined premixed metal combustor: Metal flame stabilization dynamics and nitrogen oxides production

This work presents a study of a magnesium/air combustion process in the context of innovative zero carbon dioxide (CO₂) energy carriers for reducing global warming effects. In order to analyze more deeply the confined combustion of magnesium under fluctuating overpressure conditions (0 to 24 hPa) and the generated gaseous by-products, magnesium/air flames have been realized in a combustion chamber with a conical bluff-body as flame holder and different contraction ratios diaphragms at the exit duct. Sieved magnesium samples with two size-fractions were tested: 20–50?µm and 50–70?µm. The gaseous emissions of nitrogen oxides (NO_x) and dioxygen (O₂) were analyzed with on-line infrared, ultraviolet and paramagnetic analyzers. A flame pulsating behavior was clearly observed from light emission intensity (monitored by a photodiode) and pressure fluctuations (monitored by a pressure sensor); the frequencies obtained ranged between 3 and 10?Hz. The frequency of the pulsation exhibited strong dependence on the geometric configuration of the chamber: a contraction diaphragm divided by two the frequency level of the fluctuations in the studied range of maximum overpressure. Such fluctuations may probably be the consequence of periodic perturbations of the recirculation zone behind the bluff-body. These periodic perturbations are themselves caused by strong periodic overpressure variations due to stiff contraction downstream responding to gas velocity fluctuations. This feed-back-loop mechanism was considered in this study. NO_x emissions produced through the thermal pathway were analyzed for equivalence ratios ranging from 0.29 to 1. The representation of NO_x versus equivalence ratio exhibited a parabolic shape with a maximum for an equivalence ratio of 0.4. Moreover, NO_x emissions of this metal combustor have shown a similar order of magnitude than current internal combustion engines.