Wheat Domestication Accelerated Evolution and Triggered Positive Selection in the β-Xylosidase Enzyme of Mycosphaerella graminicola

Plant cell wall degrading enzymes (PCWDEs) of plant pathogens are receiving increasing interest for their potential to trigger plant defense reactions. In an antagonistic co-evolutionary arms race between host and pathogen, PCWDEs could be under strong selection. Here, we tested the hypothesis that PCWDEs in the fungal wheat pathogen Mycosphaerella graminicola have been positively selected by analyzing ratios of non-synonymous and synonymous nucleotide changes in the genes encoding these enzymes. Analyses of five PCWDEs demonstrated that one (β-xylosidase) has been under strong positive selection and experienced an accelerated rate of evolution. In contrast, PCWDEs in the closest relatives of M. graminicola collected from wild grasses did not show evidence for selection or deviation from a molecular clock. Since the genealogical divergence of M. graminicola from these latter species coincided with the onset of agriculture, we hypothesize that the recent domestication of the host plant and/or agricultural practices triggered positive selection in β-xylosidase and that this enzyme played a key role in the emergence of a host-specialized pathogen

Biocontrol Potential of Forest Tree Endophytes

Peer reviewe

Comparison Of Heat Transfer Uniformity Of A Narrow Impingement Channel

Impingement channel cooling shows great potential for removing large amounts of heat from turbine airfoils. This highly efficient cooling process has the drawback, however, of yielding large gradients in heat transfer coefficients in the vicinity of the jet stagnation region. These variations can potentially lead to thermal gradients and stresses, when designed into a machine. It is therefore important to investigate not only the heat transfer performance of these channels, but the uniformity of their distributions as well. This paper examines the local and averaged effects of channel height in the presence of side walls on heat transfer coefficients and heat transfer coefficient uniformity. High resolution local temperature distributions on target and side wall surfaces were measured using temperature sensitive paint and recorded via a scientific grade charge-coupled device (CCD) camera, and compared to available literature. Streamwise pressure distributions were recorded and used to explain heat transfer trends. Results are presented for average jet based Reynolds numbers between 17,000 and 45,000. All experiments were carried out on a large scale single row, 15 hole impingement channel, with X/D of 5, Y/D of 4, and Z/D of 1, 3 and 5. Results showed that the channel with a medium channel height, and high Reynolds number yields both high heat transfer coefficients, as well as very uniform profiles. © 2009 by the American Institute of Aeronautics and Astronautics, Inc

Modeling Of Microscale Gas Flows In Transition Regime Part I: Flow Over Backward Facing Steps

Design of thermal management solutions for future nanoscale electronics or photonics devices will require knowledge of flow and transport through micron-scale ducts. This article concentrates on a typical flow process, namely flow over a backward-facing step with pressure boundary conditions at inlet and exit. Discrete simulation Monte Carlo (DSMC) is used as the simulation tool. An IP method is used to separate the macroscopic velocity from the molecular velocity, thus reducing statistical noise as typical in DSMC calculation of low-speed flows. Simulation is conducted for Re of 0.03 to 0.64, Ma of 0.013 to 0.083, and Kn of 0.24 to 4.81. For these parameter values no recirculating region is observed, and the high heat flux associated with reattachment is also absent

Effect Of Coriolis And Centrifugal Forces On Turbulence And Transport At High Rotation And Buoyancy Nubmers In Internal Cooling U-Channels With Smooth Walls

Numerical simulation of fluid flow and heat transfer for high rotation and buoyancy numbers flow in internal cooling channels with smooth walls of turbine blades is the main focus of this study. The flow in theses channels is affected by Rotation, buoyancy, bends and boundary conditions. On the basis of comparison between two-equation (k - ε and k - ω) and RSM turbulence models, it is concluded that the two-equation turbulence models cannot predict heat transfer correctly, while RSM showed improved prediction. Thus RSM model with either wall functions or enhanced near wall treatment was validated against available experimental data (which are primarily at low rotation and buoyancy numbers). The model was then used for cases with high rotation numbers (as much as 1.29) and high-density ratios (up to 0.4). Particular attention was given to how Reynolds stresses, turbulence intensity and transport are affected by coriolis and buoyancy/centrifugal forces caused by high levels of rotation and density ratio. The results obtained are explained in view of physical interpretation of coriolis and centrifugal forces

Simulation Of A Rectangular Cylinder In Cross Flow In A Microchannel Using Information Preservation (Ip) Method

A numerical simulation is performed to study the characteristics of the gas flow over a constant temperature rectangular cylinder in a cross flow in a micro channel. The non-isothermal Information Preservation (IP) method is employed to eliminate the statistical scatter of Direct Simulation Monte Carlo (DSMC) at low Reynolds numbers. Pressure boundary conditions based on the characteristic theory are implemented in the algorithm. The simulation results are compared with the references available in the literature. This study will form a base for our future particle-atomistic hybrid computations

Pressure Drop And Endwall Heat Transfer Effects Of A Staggered Array Of Porous Metal Pins

This paper examines the local and averaged endwall heat transfer effects of a staggered array of porous aluminum pin fins with a pore density of 10 pores per inch (PPI). The pressure drop through the channel was also determined for several flow rates. Local heat transfer coefficients on the endwall were measured using Thermochromatic Liquid Crystal (TLC) sheets recorded with a charge-coupled device (CCD) camera. Static and total pressure measurements were taken at the entrance and exit of the test section to determine the overall pressure drop through the channel and explain the heat transfer trends through the channel. Results are presented for Reynolds numbers between 18000 and 100000 and a blockage ratio (blocked channel area divided by open channel area) of 50%. All results were compared to the corresponding results obtained using solid pins. All experiments were carried out in a 150 mm by 500 mm channel with an X/D of 1.72, a Y/D of 2.0, and a Z/D of 1.72

Effect Of Coriolis And Centrifugal Forces At High Rotation And Density Ratios

Numerical simulation of fluid flow and heat transfer of high rotation and density ratio flow in internal cooling channels of turbine blades with smooth walls is the main focus of this study. The flow in these channels is affected by rotation, buoyancy, bends, and boundary conditions. On the basis of comparison between two-equation (k-ε and k-ω) and Reynolds-stress (RSM) turbulence models, it is concluded that the two-equation turbulence models cannot predict heat transfer correctly, whereas RSM showed improved prediction. Thus RSM model was validated against available experimental data (which are primarily at low rotation and buoyancy numbers). The model was then used for cases with high rotation numbers (as much as 1.29) and high-density ratios (up to 0.4) not studied previously. Particular attention was given to how Reynolds stresses, turbulence intensity, and transport are affected by coriolis and buoyancy/centrifugal forces caused by high levels of rotation and density ratio. The results obtained are explained in view of physical interpretation of Coriolis and centrifugal forces. It has been concluded that the heat-transfer rate can be enhanced rapidly by increasing rotation number to values that are comparable to the enhancement caused by introduction of ribs inside internal cooling channels. It is possible to derive linear correlation for the increase in Nusselt number as a function of rotation number. Increasing density ratios at high rotation number does not necessarily cause an increase in Nusselt number. The increasing thermal boundary-layer thickness near walls is the possible reason for this behavior of Nusselt number

Internal Cooling Using Porous Turbulators: Heat Transfer And Pressure Drop Measurements Srikrishna Mahadevan1

Heat transfer and pressure drop characteristics were studied in a low aspect ratio channel with high temperature carbon foams. The convoluted fluid flow path that significantly increases the surface area is a primary reason for the high heat transfer augmentation. The experiment provided module-averaged heat transfer coefficients on the heated wall, from which the Nusselt number was calculated. Increasing the channel blockage increased the heat transfer coefficient due to the amplification in the surface area. On the contrary, the pressure drop was also high for a high channel blockage. By using a corrugated foam arrangement, heat transfer remained relatively high with a pressure drop reduction by a factor of four. The staggered arrangement of the porous foam continuously perturbs the thermal boundary layer, which helps to sustain a high thermal gradient between the hot wall and the fluid. Increased Reynolds numbers resulted in a corresponding rise in the heat transfer rate while the roughened to smooth wall heat transfer ratio decreased