Ozonolysis of isoprene, the most abundant volatile organic compounds emitted into the Earth's troposphere after methane, yields three distinct Criegee intermediates. Among these, methyl vinyl ketone oxide (MVK-oxide) is predicted to be the major source of atmospheric hydroxyl radicals (OH) from isoprene ozonolysis. Previously, Barber et al. [J. Am. Chem. Soc., 2018, 140, pp 10866−10880] demonstrated that syn-MVK-oxide conformers undergo unimolecular decay via 1,4-hydrogen (H) transfer from the methyl group to the adjacent terminal oxygen atom, followed by the prompt release of OH radical products. Here, we selectively deuterate the methyl group of MVK-oxide (d 3 -MVK-oxide) and record its IR action spectrum in the vinyl CH stretch overtone (2ν CH ) region. The resultant time-dependent appearance of OD radical products, detected by laser-induced fluorescence, demonstrates that a unimolecular decay of d 3 -MVK-oxide proceeds by an analogous 1,4-deuterium (D) atom transfer mechanism anticipated for syn conformers. The experimental spectral and temporal results are compared with the calculated IR absorption spectrum and unimolecular decay rates predicted by the Rice−Ramsperger− Kassel−Marcus (RRKM) theory for syn-d 3 -MVK-oxide, as well as the prior study on syn-MVK-oxide. The d 3 -MVK-oxide IR action spectrum is similar to that for MVK-oxide, yet exhibits notable changes as the overtone and combination transitions involving CD stretch shift to a lower frequency. The unimolecular decay rate for d 3 -MVK-oxide is predicted to be a factor of 40 times slower than that for MVK-oxide in the 2ν CH region. Experimentally, the temporal profile of the OD products reflects the slower unimolecular decay of d 3 -MVK-oxide compared to that for MVK-oxide to OH products as well as experimental factors. Both experiment and theory demonstrate that quantum mechanical tunneling plays a very important role in the 1,4-H/D-transfer processes at energies in the vicinity of the transition-state barrier. The similarities of the IR action spectra and changes in the unimolecular decay dynamics upon deuteration indicate that syn conformers make the main contribution to the IR action spectra of MVK-oxide and d 3 -MVKoxide.
Because of its excellent small sample learning abilities and simple network structure, support vector machine (SVM) is widely applied in various pattern recognition fields, e.g., face recognition, scene classification, fault diagnosis, etc. Due to the complexity and diversity of analog circuit faults, the diagnosis accuracy and stability of SVM classifier optimized by traditional particle swarm optimization (PSO) are unsatisfactory. Therefore, this paper proposes an improved hybrid particle swarm optimization (IH-PSO) algorithm to optimize SVM, which is applied in the fault diagnosis of analog circuits. Compared with the traditional PSO algorithm, the proposed IH-PSO mainly has three improvements, namely, the oppositionbased learning population initialization, the nonlinear time-varying inertia weight, and the new position updating strategy with a spiral convergence mechanism. The performance of the proposed IH-PSO algorithm is verified by 12 commonly used benchmark functions and experimental results show that the proposed IH-PSO algorithm overcomes the deficiencies of the traditional PSO algorithm, such as slow convergence speed and trapping into local optimums. In addition, to further verify the performance of IH-PSO algorithm, the IH-PSO optimized SVM is applied to solve analog circuits fault diagnosis problems. Extensive experiments are carried out and results indicate that the proposed method has better performances both in diagnosis accuracy and stability compared with that of the traditional method.
Due to the adverse health effects and the role in the formation of secondary organic aerosols, hydroxyl radical (OH) generation by atmospheric fine particulate matter (PM) has been of particular research interest in both bulk solutions and the gas phase. However, OH generation by PM at the air−water interface of atmospheric water droplets, a unique environment where reactions can be accelerated by orders of magnitude, has long been overlooked. Using the field-induced droplet ionization mass spectrometry methodology that selectively samples molecules at the air−water interface, here, we show significant oxidation of amphiphilic lipids and isoprene mediated by water-soluble PM 2.5 at the air−water interface under ultraviolet A irradiation, with the OH generation rate estimated to be 1.5 × 10 16 molecule•s −1 •m −2 . Atomistic molecular dynamics simulations support the counter-intuitive affinity for the air−water interface of isoprene. We opine that it is the carboxylic chelators of the surface-active molecules in PM that enrich photocatalytic metals such as iron at the air−water interface and greatly enhance the OH generation therein. This work provides a potential new heterogeneous OH generation channel in the atmosphere.
It is well-known that the aqueous-phase processing of chlorine nitrate (ClONO 2 ) plays a crucial role in ozone depletion. However, many of the physical and chemical properties of ClONO 2 at the air−water interface or in bulk water are unknown or not understood on a microscopic scale. Here, the solvation and hydrolysis of ClONO 2 at the air−water interface and in bulk water at 300 K were investigated by classical and ab initio molecular dynamics (AIMD) simulations combined with free energy methods. Our results revealed that ClONO 2 prefers to accumulate at the air−water interface rather than in the bulk phase. Specifically, halogen bonding interactions (ClONO 2 )Cl•••O(H 2 O) were found to be the predominant interactions between ClONO 2 and H 2 O. Moreover, metadynamics-biased AIMD simulations revealed that ClONO 2 hydrolysis is catalyzed at the air−water interface with an activation barrier of only ∼0.2 kcal/mol; additionally, the difference in free energy between the product and reactant is only ∼0.1 kcal/mol. Surprisingly, the near-barrierless reaction and the comparable free energies of the reactant and product suggested that the ClONO 2 hydrolysis at the air−water interface is reversible. When the temperature is lowered from 300 to 200 K, the activation barrier for the ClONO 2 hydrolysis at the air−water interface is increased to ∼5.4 kcal/mol. These findings have important implications for the interpretation of experiments.
Abstract-This paper presents our results with the investigation of decentralized data dependency analysis among concurrently executing processes in a service-oriented environment. Distributed Process Execution Agents (PEXAs) are responsible for controlling the execution of processes that are composed of web services. PEXAs are also associated with specific distributed sites for the purpose of capturing data changes that occur at those sites in the context of service executions using DeltaEnabled Grid Services. PEXAs then exchange this information with other PEXAs to dynamically discover data dependencies that can be used to enhance recovery activities for concurrent processes that execute with relaxed isolation properties. This paper outlines the functionality of PEXAs, describing the data structures and communication mechanisms that are used to support decentralized construction of distributed process dependency graphs, demonstrating a more dynamic and intelligent approach to identifying how the failure of one process can potentially affect other concurrently executing processes.
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