The stochastic nature of combustion instabilities in practical land-based gas turbines and aeroengines combustors has seldom been investigated. It is shown here that a wealth of information about the ...constructive acoustic-flame interactions can be gained by scrutinising the effects of the inherent turbulence-induced noise, which forces the nonlinear thermoacoustic dynamics. In particular, one presents a method, based on the Fokker–Planck formalism, to identify from dynamic pressure signals the linear growth rates, the type of flame response nonlinearity and the potential defining the system acoustic energy. It is applied to and validated against experimental data measured in a lab-scale combustion chamber.
We consider an initial–boundary value problem for a singularly perturbed system of partial differential equations. We pose an inverse problem of determining an unknown initial condition based on ...additional information about the solution of the initial–boundary value problem. It is proved that using the expansion of the solution of the initial–boundary value problem in the small parameter
, one can obtain solutions approximating the solution of the inverse problem with order
or
.
The paper considers an inverse problem for a singularly perturbed integro-differential heat equation, which consists in determining the boundary condition from additional information on the solution ...of the initial-boundary value problem. It is proved that an approximate solution of the inverse problem can be obtained by using a finite number of terms in the expansion of the solution of the initial-boundary value problem in a small parameter.
We consider an initial–boundary value problem for the heat equation in which the heat conduction coefficient and one of the functions occurring in the source depend on time and are unknown. The ...problem is to determine these functions from additional information about the solution of the initial–boundary value problem. This problem is reduced to a system of nonlinear operator equations for the unknown functions. The system of nonlinear operator equations is used in the construction of an iteration method for determining the desired functions. The convergence of the iteration method is proved.
For the heat conduction equation with a singular perturbation corresponding to a small heat capacity or a small heat conductivity, inverse problems of determining the boundary or initial condition or ...the source term from additional information about the solution of the equation are considered. The possibility of using the expansion in a small parameter of the solution to the equation for the approximate solution of inverse problems is studied.
Damage to DNA via dissociative electron attachment has been well-studied in both the gas and condensed phases; however, understanding this process in bulk solution at a fundamental level is still a ...challenge. Here, we use a picosecond pulse of a high energy electron beam to generate electrons in liquid diethylene glycol and observe the electron attachment dynamics to ribothymidine at different stages of electron relaxation. Our transient spectroscopic results reveal that the quasi-free electron with energy near the conduction band effectively attaches to ribothymidine leading to a new absorbing species that is characterized in the UV-visible region. This species exhibits a nearly concentration-independent decay with a time constant of ~350 ps. From time-resolved studies under different conditions, combined with data analysis and theoretical calculations, we assign this intermediate to an excited anion radical that undergoes N1-C1' glycosidic bond dissociation rather than relaxation to its ground state.
Mathematical Models of Combustion Processes Denisov, I. V.; Denisov, A. I.
Journal of mathematical sciences (New York, N.Y.),
05/2024, Volume:
281, Issue:
3
Journal Article
Peer reviewed
In this paper, we consider model problems of chemical kinetics that lead to singularly perturbed parabolic equations in domains with nonsmooth boundaries. The solvability of such problems depends on ...the properties of the inhomogeneity at corner points of the boundary.
Among the radicals (hydroxyl radical (
OH), hydrogen atom (H
), and solvated electron (e
)) that are generated via water radiolysis,
OH has been shown to be the main transient species responsible for ...radiation damage to DNA via the indirect effect. Reactions of these radicals with DNA-model systems (bases, nucleosides, nucleotides, polynucleotides of defined sequences, single stranded (ss) and double stranded (ds) highly polymeric DNA, nucleohistones) were extensively investigated. The timescale of the reactions of these radicals with DNA-models range from nanoseconds (ns) to microseconds (µs) at ambient temperature and are controlled by diffusion or activation. However, those studies carried out in dilute solutions that model radiation damage to DNA via indirect action do not turn out to be valid in dense biological medium, where solute and water molecules are in close contact (e.g., in cellular environment). In that case, the initial species formed from water radiolysis are two radicals that are ultrashort-lived and charged: the water cation radical (H
O
) and prethermalized electron. These species are captured by target biomolecules (e.g., DNA, proteins, etc.) in competition with their inherent pathways of proton transfer and relaxation occurring in less than 1 picosecond. In addition, the direct-type effects of radiation, i.e., ionization of macromolecule plus excitations proximate to ionizations, become important. The holes (i.e., unpaired spin or cation radical sites) created by ionization undergo fast spin transfer across DNA subunits. The exploration of the above-mentioned ultrafast processes is crucial to elucidate our understanding of the mechanisms that are involved in causing DNA damage via direct-type effects of radiation. Only recently, investigations of these ultrafast processes have been attempted by studying concentrated solutions of nucleosides/tides under ambient conditions. Recent advancements of laser-driven picosecond electron accelerators have provided an opportunity to address some long-term puzzling questions in the context of direct-type and indirect effects of DNA damage. In this review, we have presented key findings that are important to elucidate mechanisms of complex processes including excess electron-mediated bond breakage and hole transfer, occurring at the single nucleoside/tide level.
A series of photoactive triads have been synthesized and investigated in order to elucidate photoinduced electron transfer and hole migration mechanism across nanosized, rigid helical foldamers. The ...triads are comprised of a central helical oligoamide foldamer bridge with 9, 14, 18, 19, or 34 8-amino-2-quinolinecarboxylic acid repeat units, and of two chromophores, an N-terminal oligo(para-phenylenevinylene) electron donor and a C-terminal perylene bis-imide electron acceptor. Time-resolved fluorescence and transient absorption spectroscopic studies showed that, following photoexcitation of the electron acceptor, fast electron transfer occurs initially from the oligoquinoline bridge to the acceptor chromophore on the picosecond time scale. The oligo(para-phenylenevinylene) electron donor is oxidized after a time delay during which the hole migrates across the foldamer from the acceptor to the donor. The charge separated state that is finally generated was found to be remarkably long-lived (>80 μs). While the initial charge injection rate is largely invariant for all foldamer lengths (ca. 60 ps), the subsequent hole transfer to the donor varies from 1 × 109 s–1 for the longest sequence to 17 × 109 s–1 for the shortest. In all cases, charge transfer is very fast considering the foldamer length. Detailed analysis of the process in different media and at varying temperatures is consistent with a hopping mechanism of hole transport through the foldamer helix, with individual hops occurring on the subpicosecond time scale (k ET = 2.5 × 1012 s–1 in CH2Cl2). This work demonstrates the possibility of fast long-range hole transfer over 300 Å (through bonds) across a synthetic modular bridge, an achievement that had been previously observed principally with DNA structures.
Abstract
Time-resolved identification of surface-bound intermediates on metallic nanocatalysts is imperative to develop an accurate understanding of the elementary steps of CO
2
reduction. Direct ...observation on initial electron transfer to CO
2
to form surface-bound CO
2
•−
radicals is lacking due to the technical challenges. Here, we use picosecond pulse radiolysis to generate CO
2
•
−
via aqueous electron attachment and observe the stabilization processes toward well-defined nanoscale metallic sites. The time-resolved method combined with molecular simulations identifies surface-bound intermediates with characteristic transient absorption bands and distinct kinetics from nanosecond to the second timescale for three typical metallic nanocatalysts: Cu, Au, and Ni. The interfacial interactions are further investigated by varying the important factors, such as catalyst size and the presence of cation in the electrolyte. This work highlights fundamental ultrafast spectroscopy to clarify the critical initial step in the CO
2
catalytic reduction mechanism.
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