Heat and mass transports through a rough surface are among the most fundamental and important phenomena in either natural or engineering problems. In this paper, theoretical modelling and direct simulation Monte Carlo method are employed to study the heterogeneous reaction–diffusion features induced by microscale roughness which is comparable to the molecular mean free path of the ambient gas. A quasi-one-dimensional homogeneous model is proposed, and it consists of an external diffusion region outside the roughness elements and an internal reaction–diffusion region which could be equivalent to a smooth surface with an effective chemical property. The external macroscopic diffusion can be characterized by a non-equilibrium criterion – the Damköhler number. The internal diffusion in micro-cavities must be analysed by considering the rarefied gas effects on the diffusivity, and another non-equilibrium criterion, the Thiele number, is introduced to evaluate the effective boundary condition imposed on the external region. Analytical formulae based on these criteria are derived to predict the equivalent surface reaction–diffusion performance, and the predictions compare well with the numerical results of different types of surface reaction, even on the three-dimensional roughness. This reveals that the roughness could either enhance or weaken the apparent reaction rate depending on the non-equilibrium degree. This study could enrich our understanding of the gas–surface interactions on a rough wall, such as the oxidation, catalysis and energy accommodation, and also preliminarily provides a practical method for evaluation of the aerothermochemical performance of coating materials of hypersonic vehicles.
Objective: The transformation system for the asparagus stem blight pathogen Phomopsis asparagi (Sacc.) Bubak has not yet been reported. In the present study, we intend to achieve and optimize the genetic transformation of P. asparagi. This study aims at establishing the foundation for understanding the pathogenic mechanism of P. asparagi, which will be of great theoretical and practical significance.Methods: The Agrobacterium tumefaciens-mediated transformation (ATMT) system for P. asparagi was constructed at three aspects, i.e. condition optimization, insertion verification and transformant stability.Results: The optimal conditions for this ATMT system were as follows: 8 h of pre-induction, 48 h of co-culture, 200 μmol/L AS in ISM, co-culture at 25-28°C and pH 5.6-5.8 of ISM at the co-culture phase. The PCR result of the hph gene revealed that an expected band of about 500 bp was amplified from all the 10 transformants selected at random, and the PCR result of the Vir gene revealed that an expected band of about 730 bp was amplified from the four strains of A. tumefacien as positive controls, whereas no corresponding DNA band could be amplified from the 10 transformants. The results of the two PCR amplifications clearly showed that T-DNA was indeed inserted into the genome of target isolate FJ2. The stability result revealed that transformants still displayed high resistance to hygromycin B and could grow normally after subculture for five generations.Conclusion: A stable and efficient ATMT transformation system for P. asparagus was constructed systematically, in which a high transformation rate was achieved. For improving this system, the trasformation conditions were optimized through gradient experiments, T-DNA insertion was verified through dual PCR and the insertion segment containing hph gene in the transformant was proved hereditary stable through subculture. This system layed a foundation for the research on pathogenic mechanism and pathogenicity-related genes of P. asparagi.
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