Solving chromatographic challenges in comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry using multivariate curve resolution–alternating least squares

Multivariate curve resolution–alternating least squares (MCR–ALS) analysis is proposed to solve chromatographic challenges during two-dimensional gas chromatography–time-of-flight mass spectrometry (GC?×?GC–TOFMS) analysis of complex samples, such as crude oil extract. In view of the fact that the MCR–ALS method is based on the fulfillment of the bilinear model assumption, three-way and four-way GC?×?GC–TOFMS data are preferably arranged in a column-wise superaugmented data matrix in which mass-to-charge ratios (m/z) are in its columns and the elution times in the second and first chromatographic columns are in its rows. Since m/z values are common for all measured spectra in all second-column modulations, unavoidable chromatographic challenges such as retention time shifts within and between GC?×?GC–TOFMS experiments are properly handled. In addition, baseline/background contributions can be modeled by adding extra components to the MCR–ALS model. Another outstanding aspect of MCR–ALS analysis is its extreme flexibility to consider all samples (standards, unknowns, and replicates) in a single superaugmented data matrix, allowing joint analysis. In this way, resolution, identification, and quantification results can be simultaneously obtained in a very fast and reliable way. The potential of MCR–ALS analysis is demonstrated in GC?×?GC–TOFMS analysis of a North Sea crude oil extract sample with relative errors in estimated concentrations of target compounds below 6.0 % and relative standard deviations lower than 7.0 %. The results obtained, along with reasonable values for the lack of fit of the MCR–ALS model and high values of the reversed match factor in mass spectra similarity searches, confirm the reliability of the proposed strategy for GC?×?GC–TOFMS data analysis.      

Spontaneous emission and spectral properties of radiation by relativistic electrons in a gyro‐klystron and optical‐klystron undulator

In this paper spontaneous emission of radiation by relativistic electrons in a gyro‐klystron is studied. The scheme consists of two solenoid sections separated by a dispersive section. In the dispersive section the electrons are made non‐resonant with the radiation. The dispersive section transforms a small change of the velocity into changes of the phases of the electrons. This leads to enhanced radiation due to klystron‐type modulation as compared with a conventional gyrotron‐type device driven by cyclotron maser interaction. It is shown that the klystron‐modulated spectrum depends on the dispersive field strength, finite perpendicular velocity component and length of the solenoids but is independent of the axial magnetic field strength. A simple scheme to design a gyro‐klystron is discussed.     

Theoretical modeling of electrochemical interactions in bimetallic molybdenum nitrosyl complexes incorporating saturated bridges

Hybrid B3LYP and non-hybrid OLYP DFT formalism has been applied to neutral and reduced forms of bimetallic hydrotris(3-methylpyrazol-1-yl)borato (Tp^3-Me) molybdenum nitrosyl complexes incorporating ethane-1,2-diolate bridges. Direct evidence for localization of an extra electron in mixed-valence compounds {16e:17e}⁻ is based on the analysis of electron density, energetic stabilization of asymmetric structures with an electron trapped on one Mo and the splitting of both calculated and experimental ν_NO stretching frequencies. Differences in the first and second electron affinities calculated in PCM solvent model have been successfully related to cyclic voltammetry measurements. Electronic interactions through saturated ethanediolato bridges are evidenced by the extent of spin density delocalization towards the second Mo center.     

Amino-sugar modular ligands-useful cores for the formation of asymmetric copper 1,4-addition catalysts

Modular phosphine ligands, synthesised rapidly from commercial N-acetylglucosamine, are very effective in copper(i)-catalysed 1,4-additions of ZnR(2) to linear aliphatic enones (87-95% ee).     

Dependence of the Lifetime upon the Excitation Energy and Intramolecular Energy Transfer Rates: The (5) D(0) Eu(III) Emission Case

In many Eu(III) -based materials, the presence of an intermediate energy level, such as ligand-to-metal charge transfer (LMCT) states or defects, that mediates the energy transfer mechanisms can strongly affect the lifetime of the (5) D(0) state, mainly at near-resonance (large transfer rates). We present results for the dependence of the (5) D(0) lifetime on the excitation wavelength for a wide class of Eu(III) -based compounds: ionic salts, polyoxometalates (POMs), core/shell inorganic nanoparticles (NPs) and nanotubes, coordination polymers, β-diketonate complexes, organic-inorganic hybrids, macro-mesocellular foams, functionalized mesoporous silica, and layered double hydroxides (LDHs). This yet unexplained behavior is successfully modelled by a coupled set of rate equations with seven states, in which the wavelength dependence is simulated by varying the intramolecular energy transfer rates. In addition, the simulations of the rate equations for four- and three-level systems show a strong dependence of the emission lifetime upon the excitation wavelength if near-resonant non-radiative energy transfer processes are present, indicating that the proposed scheme can be generalized to other trivalent lanthanide ions, as observed for Tb(III) /Ce(III) . Finally, the proper use of lifetime definition in the presence of energy transfer is emphasized.     

Efficient solutions to robust, semi-implicit discretizations of the immersed boundary method

The immersed boundary method is a versatile tool for the investigation of flow-structure interaction. In a large number of applications, the immersed boundaries or structures are very stiff and strong tangential forces on these interfaces induce a well-known, severe time-step restriction for explicit discretizations. This excessive stability constraint can be removed with fully implicit or suitable semi-implicit schemes but at a seemingly prohibitive computational cost. While economical alternatives have been proposed recently for some special cases, there is a practical need for a computationally efficient approach that can be applied more broadly. In this context, we revisit a robust semi-implicit discretization introduced by Peskin in the late 1970s which has received renewed attention recently. This discretization, in which the spreading and interpolation operators are lagged, leads to a linear system of equations for the interface configuration at the future time, when the interfacial force is linear. However, this linear system is large and dense and thus it is challenging to streamline its solution. Moreover, while the same linear system or one of similar structure could potentially be used in Newton-type iterations, nonlinear and highly stiff immersed structures pose additional challenges to iterative methods. In this work, we address these problems and propose cost-effective computational strategies for solving Peskin’s lagged-operators type of discretization. We do this by first constructing a sufficiently accurate approximation to the system’s matrix and we obtain a rigorous estimate for this approximation. This matrix is expeditiously computed by using a combination of pre-calculated values and interpolation. The availability of a matrix allows for more efficient matrix–vector products and facilitates the design of effective iterative schemes. We propose efficient iterative approaches to deal with both linear and nonlinear interfacial forces and simple or complex immersed structures with tethered or untethered points. One of these iterative approaches employs a splitting in which we first solve a linear problem for the interfacial force and then we use a nonlinear iteration to find the interface configuration corresponding to this force. We demonstrate that the proposed approach is several orders of magnitude more efficient than the standard explicit method. In addition to considering the standard elliptical drop test case, we show both the robustness and efficacy of the proposed methodology with a 2D model of a heart valve.     

Three-dimensional,fully adaptive simulations of phase-field fluid models

We present an efficient numerical methodology for the 3D computation of incompressible multi-phase flows described by conservative phase-field models. We focus here on the case of density matched fluids with different viscosity (Model H). The numerical method employs adaptive mesh refinements (AMR) in concert with an efficient semi-implicit time discretization strategy and a linear, multi-level multigrid to relax high order stability constraints and to capture the flow’s disparate scales at optimal cost. Only five linear solvers are needed per time-step. Moreover, all the adaptive methodology is constructed from scratch to allow a systematic investigation of the key aspects of AMR in a conservative, phase-field setting. We validate the method and demonstrate its capabilities and efficacy with important examples of drop deformation, Kelvin–Helmholtz instability, and flow-induced drop coalescence.     

New polycyclic pyran ring systems

Reaction of 1-oxo-3-dialkylamino-1H-naphtho[2,1-b]pyrans, 4-hydroxycoumarin and formaldehyde gave rise to the formation of 1-oxo-2-((2-oxo-4′-hydroxy-2′H-1′-benzopyran-3′-yl)-melhyl J-3-dialkylamino-1H-naphtho[2,1-b]pyrans. When these compounds were refluxed in glacial acetic acid, cyclization occurred and 6,8-dioxo-6H,7H,07-,5,15,16-trioxadibenzo[a,j]-naphthacene arose by cleavage of the dialkylamino group. In a similar manner, starting from suitable products, many other trioxanaphthacene or azadioxanaphthacene derivatives were synthesized.