An EOX method for the detection of halogenated hydrocarbons in soil samples

Analytical and Bioanalytical Chemistry -     

Ignition of dimethyl ether/air mixtures by hot particles: Impact of low temperature chemical reactions

Understanding and characterizing ignition of flammable mixtures by hot particles is important for assessing and reducing the risk of accidental ignition and explosion in industry and aviation. Recently, many studies have been conducted for ignition of gaseous mixtures by hot particles. However, the effects of low-temperature chemistry (LTC) on ignition by hot particles received little attention. LTC plays an important role in the ignition of most hydrocarbon fuels and may induce cool flames. The present study aims to numerically assess the effects of LTC on ignition by the hot particles. We consider the transient ignition processes induced by a hot spherical particle in quiescent and flowing stoichiometric dimethyl ether/air mixtures. 1D and 2D simulations, respectively, are conducted for the ignition process by hot-particles in quiescent and flowing mixtures. A detailed kinetic model including both LTC and high-temperature chemistry (HTC) is used in simulations. The results exhibit a premixed cool flame to be first initiated by the hot particle. Then a double-flame structure with both premixed cool and hot flames is observed at certain conditions. At zero or low inlet flow velocities, the hot flame catches up and merges with the leading cool flame. At high inlet flow velocities, the hot flame cannot be initiated due to the short residence time and large convective loss of heat and radicals. Comparing the results with and without considering LTC confirms that LTC accelerates substantially ignition via HTC in a certain range of hot particle temperatures. The mechanism of ignition promotion by LTC is interpreted by analyzing the radical pool produced by the LTC and HTC surrounding the hot particle. Moreover, the influence of inlet flow velocity on ignition by hot particles is assessed. Non-monotonic change of ignition delay time with flow velocity is observed and discussed.     

2‐Amino‐8‐(2‐deoxy‐2‐fluoro‐β‐d‐arabinofuranosyl)imidazo[1,2‐a][1,3,5]triazin‐4(8H)‐one monohydrate,a 2′‐deoxyguanosine analogue with an altered Watson–Crick recognition site

The title compound, C₁₀H₁₂FN₅O₄·H₂O, shows an anti glycosyl orientation [χ = −123.1 (2)°]. The 2‐deoxy‐2‐fluoroarabinofuranosyl moiety exhibits a major C2′‐endo sugar puckering (S‐type, C2′‐endo–C1′‐exo, ²T₁), with P = 156.9 (2)° and τ_m = 36.8 (1)°, while in solution a predominantly N conformation of the sugar moiety is observed. The conformation around the exocyclic C4′—C5′ bond is −sc (trans, gauche), with γ = −78.3 (2)°. Both nucleoside and solvent molecules participate in the formation of a three‐dimensional hydrogen‐bonding pattern via intermolecular N—H...O and O—H...O hydrogen bonds; the N atoms of the heterocyclic moiety and the F substituent do not take part in hydrogen bonding.     

On the trimerization of cyanoacetylene: mechanism of formation of tricyanobenzene isomers and laboratory detection of their radio spectra

In support of a deeper understanding of the chemistry of cyanoacetylene--a known constituent of planetary atmospheres and interstellar space--theoretical and experimental studies address the chemical mechanism of dimerization and trimerization, and provide high-resolution rotational spectra of two of the trimeric products, 1,2,3- and 1,2,4-tricyanobenzene. Analysis of the rotational spectra is particularly challenging because of quadrupolar coupling from three (14)N nuclei. The laboratory rotational spectra provide the basis for future searches for these polar aromatic compounds in interstellar space by radio astronomy.     

The extended finite element method for two-phase and free-surface flows: A systematic study

In immiscible two-phase flows, jumps or kinks are present in the velocity and pressure fields across the interfaces of the two fluids. The extended finite element method (XFEM) is able to reproduce such discontinuities within elements. Robust and accurate interface capturing schemes with no restrictions on the interface topology are thereby enabled. This paper investigates different enrichment schemes and time-integration schemes within the XFEM. Test cases with and without surface tension on moving or stationary meshes are studied and compared to interface tracking results when possible. A particularly useful setting is extracted which is recommended for two-phase flows. An extension of this formulation for the simulation of free-surface flows and of floating objects is proposed.     

Interface model for non-equilibrium evaporation

A microscopic interface condition for condensing/evaporating interfaces is developed by combining a velocity dependent condensation probability [T. Tsuruta, H. Tanaka, T. Masuoka, Int. J. Heat Mass Transfer 42 (1999) 4107] and Maxwell type interface conditions with accommodation. Using methods from kinetic theory, macroscopic interface conditions for mass and energy transport across the phase boundary are derived. This model only applies to simple substances, where diffusive effects in the bulk phases are not present. The results are compared to classical non-equilibrium thermodynamics. The interface conditions are considered for the limit of small deviation from equilibrium, and the corresponding Onsager coefficients are computed. These results are useful as boundary conditions for non-equilibrium evaporation and condensation problems, as done previously by our group [M. Bond, H. Struchtrup, Phys. Rev. E 70 (2004) 061605].     

Lorentz spaces with variable exponents

We introduce Lorentz spaces and with variable exponents. We prove several basic properties of these spaces including embeddings and the identity . We also show that these spaces arise through real interpolation between and . Furthermore, we answer in a negative way the question posed in 12 whether the Marcinkiewicz interpolation theorem holds in the frame of Lebesgue spaces with variable integrability.     

Simultaneous Domination in Graphs

Let \({F_1, F_2, \ldots, F_k}\) be graphs with the same vertex set V. A subset \({S \subseteq V}\) is a simultaneous dominating set if for every i, 1 ≤ i ≤ k, every vertex of F _i not in S is adjacent to a vertex in S in F _i ; that is, the set S is simultaneously a dominating set in each graph F _i . The cardinality of a smallest such set is the simultaneous domination number. We present general upper bounds on the simultaneous domination number. We investigate bounds in special cases, including the cases when the factors, F _i , are r-regular or the disjoint union of copies of K _r . Further we study the case when each factor is a cycle.     

Distinguishing-Transversal in Hypergraphs and Identifying Open Codes in Cubic Graphs

The open neighborhood N(v) of a vertex v in a graph G is the set of vertices adjacent to v in G. A graph is twin-free (or open identifiable) if every two distinct vertices have distinct open neighborhoods. A separating open code in G is a set C of vertices such that \({N(u) \cap C \neq N(v) \cap C}\) for all distinct vertices u and v in G. An open dominating set, or total dominating set, in G is a set C of vertices such that \({N(u) \cap C \ne N(v) \cap C}\) for all vertices v in G. An identifying open code of G is a set C that is both a separating open code and an open dominating set. A graph has an identifying open code if and only if it is twin-free. If G is twin-free, we denote by \({\gamma^{\rm IOC}(G)}\) the minimum cardinality of an identifying open code in G. A hypergraph H is identifiable if every two edges in H are distinct. A distinguishing-transversal T in an identifiable hypergraph H is a subset T of vertices in H that has a nonempty intersection with every edge of H (that is, T is a transversal in H) such that T distinguishes the edges, that is, \({e \cap T \neq f \cap T}\) for every two distinct edges e and f in H. The distinguishing-transversal number \({\tau_D(H)}\) of H is the minimum size of a distinguishing-transversal in H. We show that if H is a 3-uniform identifiable hypergraph of order n and size m with maximum degree at most 3, then \({20\tau_D(H) \leq 12n + 3m}\) . Using this result, we then show that if G is a twin-free cubic graph on n vertices, then \({\gamma^{\rm IOC}(G) \leq 3n/4}\) . This bound is achieved, for example, by the hypercube.