Identification and Characterization of the Anti-Methicillin-Resistant \u3ci\u3eStaphylococcus aureus\u3c/i\u3e WAP-8294A2 Biosynthetic Gene Cluster from \u3ci\u3eLysobacter enzymogenes\u3c/i\u3e OH11

Lysobactor enzymogenes strain OH11 is an emerging biological control agent of fungal and bacterial diseases. We recently completed its genome sequence and found it contains a large number of gene clusters putatively responsible for the biosynthesis of nonribosomal peptides and polyketides, including the previously identified antifungal dihydromaltophilin (HSAF). One of the gene clusters contains two huge open reading frames, together encoding 12 modules of nonribosomal peptide synthetases (NRPS). Gene disruption of one of the NRPS led to the disappearance of a metabolite produced in the wild type and the elimination of its antibacterial activity. The metabolite and antibacterial activity were also affected by the disruption of some of the flanking genes. We subsequently isolated this metabolite and subjected it to spectroscopic analysis. The mass spectrometry and nuclear magnetic resonance data showed that its chemical structure is identical to WAP-8294A2, a cyclic lipodepsipeptide with potent antimethicillin-resistant Staphylococcus aureus (MRSA) activity and currently in phase I/II clinical trials. The WAP- 8294A2 biosynthetic genes had not been described previously. So far, the Gram-positive Streptomyces have been the primary source of anti-infectives. Lysobacter are Gram-negative soil/water bacteria that are genetically amendable and have not been well exploited. The WAP-8294A2 synthetase represents one of the largest NRPS complexes, consisting of 45 functional domains. The identification of these genes sets the foundation for the study of the WAP-8294A2 biosynthetic mechanism and opens the door for producing new anti-MRSA antibiotics through biosynthetic engineering in this new source of Lysobacter

Large eddy simulation of ignition and combustion of ethylene/air turbulent jet diffusion flame with reduced kinetic mechanism

In this paper, unsteady process of ignition and combustion of turbulent plane-jet diffusion flame of ethylene/air at varied fuel/air ratios is numerically simulated with Large Eddy Simulation (LES) and a reduced kinetic mechanism of ethylene. The kinetic mechanism consisting of 25species and 131steps is reduced from a 71species/395steps detailed mechanism via the method of error-propagation-based directed relation graph (DRGEP) and sensitivity analysis. The LES results of height of flame lift-up and averaged temperature profiles at different downstream locations are compared with the DNS result of Yoo (2011) and satisfactory agreements are found. Unsteady processes of ignition and combustion of ethylene plane-jet diffusion flame are simulated with varied fuel injection velocities. Dynamic evolutions of temperature field as well as CH2 and OH radicals are obtained, which are found to be strongly related to turbulence eddies caused by jet/air mixing layer. The present numerical study shows that LES method with reduced mechanism of hydrocarbon fuels can effectively simulate temporal and spatial evolution of ignition and combustion process. © 2015, AIAA American Institute of Aeronautics and Astronautics. All rights reserved

Development of efficient and accurate skeletal mechanisms for hydrocarbon fuels and kerosene surrogate

In this paper, the methodology of the directed relation graph with error propagation and sensitivity analysis (DRGEPSA), proposed by Niemeyer et al. [Combustion and Flame 157 2010) 1760–1770], and its differences to the original directed relation graph method are described. Using DRGEPSA, the detailed mechanism of ethylene containing 71 species and 395 reaction steps is reduced to several skeletal mechanisms with different error thresholds. The 25-species and 131-step mechanism and the 24-species and 115-step mechanism are found to be accurate for the predictions of ignition delay time and laminar flame speed. Although further reduction leads to a smaller skeletal mechanism with 19 species and 68 steps, it is no longer able to represent the correct reaction processes. With the DRGEPSA method, a detailed mechanism for n-dodecane considering low-temperature chemistry and containing 2115 species and 8157 steps is reduced to a much smaller mechanism with 249 species and 910 steps while retaining good accuracy. If considering only high-temperature (higher than 1000 K) applications, the detailed mechanism can be simplified to even smaller mechanisms with 65 species and 340 steps or 48 species and 220 steps. Furthermore, a detailed mechanism for a kerosene surrogate having 207 species and 1592 steps is reduced with various error thresholds and the results show that the 72-species and 429-step mechanism and the 66-species and 392-step mechanism are capable of predicting correct combustion properties compared to those of the detailed mechanism. It is well recognized that kinetic mechanisms can be effectively used in computations only after they are reduced to an acceptable size level for computation capacity and at the same time retaining accuracy. Thus, the skeletal mechanisms generated from the present work are expected to be useful for the application of kinetic mechanisms of hydrocarbons to numerical simulations of turbulent or supersonic combustion.Keywords: Reduced chemistry, Hydrocarbons, Directed relation graph, Ignition delay tim

Effects of Macroparameters on the Thickness of an Interfacial Nanolayer of Al2O3- and TiO2-Water-Based Nanofluids

In this paper, thicknesses of interfacial nanolayers of alumina-deionized water (DW) and titanium dioxide-deionized water (DW) nanofluids are studied. Thermal conductivities of both nanofluids were measured in a temperature range of 298 to 353 K at particle volume ratios of 0.2 to 1.5% by experiments. A theoretical model considered both the effects of the interfacial nanolayer and Brownian motion is developed for thermal conductivity. A relational expression between nanolayer thickness and bulk temperature and volume fraction of particles of nanofluids is derived from the theoretical model. With the experimental data of thermal conductivity, changes of nanolayer thickness with nanofluids macroscopic properties (bulk temperature and particle volume ratio) are obtained. The present results show that nanolayer thickness increases with fluid temperature almost linearly and decreases with particle volume fraction in a power law. Based on the present results, simple formulas of interfacial nanolayer thickness as a function of fluid temperature and particle volume fraction are proposed for both water-based nanofluids

Numerical Study of Turbulent Convective Heat Transfer of Aviation Kerosene in Coiled Pipes

Turbulent flow and convective heat transfer of kerosene in coiled pipes with different wall boundary conditions and curvature radii of coiled pipes are numerically studied. The Reynolds-averaged Navier-Stokes equations are solved by finite volume method and the realizable k-epsilon model is applied for turbulence modeling. The fluid media is aviation kerosene with an inlet supercritical pressure of 3MPa and an inlet temperature of 400K. The present results provide temperature and velocity fields as well as distributions of turbulence kinetic energy and streamlines at different axial locations along the flow direction. The Nusselt number at the outer side of the pipe wall is higher than that at the inner side by 75%. Compared to a straight pipe with the same pipe radius of 6mm and inlet flow conditions, the coiled pipe with a curvature radius of 192.5mm can increase the averaged heat transfer coefficient by 28.5%. Meanwhile, it is found that when the curvature ratio increases, the effect of secondary flow in the cross section of pipe is more significant and the heat transfer effect at different locations of the pipe wall also changes significantly. In addition, the present results also reveal that heat transfer deterioration takes place for the kerosene flow in coiled pipe with an increased wall heat flux due to the state change of kerosene from liquid to supercritical

Experimental study on flow and heat transfer of Al-kerosene nanofuels for regenerative cooling application

In this paper, flow resistance and convective heat transfer of Al-kerosene nanofuels are studied experimentally. Al-kerosene nanofuels with mass fractions of 0.5 , 1 , and 2 g/L are prepared and applied as the flow medium for flow and heat transfer experiment via a heating facility. The experiment results indicate that the addition of aluminum nanoparticles has significant influence on both flow resistance and heat transfer performance. Compared to kerosene experiment, friction coefficient, heat transfer coefficient, and Nusselt number of Al-kerosene nanofuels all increase with different increasing rates. With a mass fraction of 1 g/L, the increase rate of friction coefficient was 11%, while the increase rate of heat transfer coefficient and Nusselt number is 19% and 12%, respectively. In order to evaluate the overall flow and heat transfer performance of Al-kerosene nanofuels, a performance evaluation criteria (PEC) is evaluated, and the present experimental results prove that the addition of aluminum nanoparticles gave a gain to the overall thermal performance of kerosene. The present study is aimed to provide useful references for regenerative cooling improvements

An analytical theory of heated duct flows in supersonic combustors

One-dimensional analytical theory is developed for supersonic duct flow with variation of cross section, wall friction, heat addition, and relations between the inlet and outlet flow parameters are obtained. By introducing a selfsimilar parameter, effects of heat releasing, wall friction, and change in cross section area on the flow can be normalized and a self-similar solution of the flow equations can be found. Based on the result of self-similar solution, the sufficient and necessary condition for the occurrence of thermal choking is derived. A relation of the maximum heat addition leading to thermal choking of the duct flow is derived as functions of area ratio, wall friction, and mass addition, which is an extension of the classic Rayleigh flow theory, where the effects of wall friction and mass addition are not considered. The present work is expected to provide fundamentals for developing an integral analytical theory for ramjets and scramjets

Effect of dimple depth on turbulent flow and heat transfer of kerosene in rectangular duct

In this paper, the coupling effect of dimple depth and fluid properties on convective heat transfer of kerosene flowing in a small-scale rectangular duct with circular dimples is studied numerically. The numerical simulation is based on Reynolds average method with a shear stress transport (SST) k-omega turbulence model and a 10-components surrogate model of kerosene. Turbulent flow and heat transfer properties in different depths of circular dimples are obtained. The results show that the three-dimensional vortices are generated by dimples and the vortices alter local turbulent flowing significantly, leading to both enhanced and reduced convective heat transfer to the wall at different locations. It is also found that the averaged Nusselt number on different dimpled walls first increases in the raising of dimple depths and then decreases after dimple depths reach a certain value. The obtained flow field shows that the heat transfer enhancement on the dimpled wall is caused by vortices with horse-shoe and tornado structures. When dimple depth further increases, the vortical structure changes to asymmetric horn spiral form, which causes heat transfer reduction. Similar to the variation of Nusselt number, the friction factor through dimpled duct also increases firstly with the dimple depth and then decreases