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A first-principles investigation of the early-stage oxidation in two Σ3 tungsten grain boundaries
No full textImpurities at the grain boundary (GB) can result in the weakening of local structures possibly leading to fracture. This work uses first-principle calculations to study the effect of interstitial oxygen (O) on two tungsten (W) symmetric tilt GBs – the Σ3 [110](112) and Σ3 [110](111). Solution energy calculations show that O is thermodynamically driven towards the GB. Migration energy analysis indicates that O must overcome large energy barriers to exit the GB, effectively trapping interstitial O at these sites. The strength of both GBs studied here was found to monotonically decrease with increasing oxygen coverage up to the point of oxide precipitation. This work found that the work of separation of a W Σ3(112) and a W Σ3(111) GB decreased by a factor of two from a pure GB to a W(112)/WO3(001) and W(111)/WO3(001) interface respectively, potentially making these regions the most vulnerable to cracking. Finally, our computations on the initial phase of the oxide growing on a metal substrate demonstrated that the crystalline oxide was thermodynamically more favorable than the amorphous oxide when two or more oxide layers existed. Establishing these structure-property relationships may help provide some insight into engineering improved structural materials. Abstract © Elsevier.
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Life and Performance Improvement Trenches
No full textA blade outer air seal assembly includes a plurality of seal segments circumferentially disposed about an array of blades rotatable about an axis, each of the plurality of seal segments having a radially inner surface facing a tip of each blade of the array of blades, the radially inner surface having an arrangement of trenches formed therein, and a radially outer surface opposite the radially inner surface. The arrangement of trenches is disposed between 30% and 80% of a chord of a blade of the array of blades as taken at the respective tip, and the arrangement of trenches is aperiodic in the axial direction
Amp: Single-shot Ultra-wide Fisheye-to-cubemap PnP Pose Estimation
No full textEstimating the position and orientation of a rigid object from an image is critical for situational awareness in robotics and autonomous systems. This study explores relative pose estimation using an ultra-wide fisheye camera for unmanned aircraft inspection vehicles. Ultra-wide fisheye lenses introduce radial distortion and capture features beyond the rectilinear image plane, rendering rectilinear Perspective-n-Point (PnP) algorithms inadequate. Designing a bespoke ultra-wide fisheye localization algorithm requires consideration of both the feature detection method and the pose estimator itself. This study proposes a novel method that combines (1) a fisheye-to-cubemap reprojection, (2) a You Only Look Once (YOLO) convolutional neural network trained for arbitrary airborne perspectives, and (3) an Angle-Agnostic and Multiple-Frame PnP (AMP) pose estimation algorithm. Our pipeline achieves a 97% success rate for valid pose estimates, with a mean absolute translational error of less than 12 cm on real ultra-wide fisheye imagery, outperforming conventional techniques, including OpenCV
UV‐Activated Advanced Oxidation of MTBE and TBA: A Comparison of Sulfate and Hydroxyl‐Radical Treatment Processes
No full textContaminated groundwater must be treated to protect drinking water supplies. This study investigated the degradation of MTBE and TBA with UV/persulfate (PS) and UV/hydrogen peroxide (H2O2) advanced oxidation processes. Experiments were conducted at initial concentrations of MTBE and TBA of 7.4 and 6.2 mg/L respectively over a range of conditions and computational analysis was carried out to elucidate reaction mechanisms and pathways. Pseudo first-order rate constants were retrieved from temporal degradation profiles. MTBE degradation was faster than that of TBA, and UV/PS-driven oxidation of both chemicals was faster than that of UV/H2O2. Relative absorptivity measurements showed that PS absorbed a higher proportion of light than H2O2 did, which in turn created greater potential to generate radicals. Density Functional Theory (DFT) results provided additional new insights. UV/PS is a promising groundwater remediation technology for the removal of MTBE and TBA
High-Speed Aircraft Stability and Control Metrics
Get PDFThis review paper identifies key stability and control screening parameters needed to design low-risk, general-purpose high-speed aircraft. These derive from MIL-STD-8785C, MIL-STD-1797, and older AGARD reports, and are suitable for assessing conceptual high-speed vehicles. We demonstrate their applicability using published ground test, computation, and flight test data from the Bell X-2, North American X-15, Martin X-24A, Northrop HL-10, Lockheed Blackbird (YF-12/SR-71), and North American XB-70 as well as the Rockwell Space Shuttle Orbiter. The relative success of the X-15 and Blackbird and the performance limitations of the others indicate the need to scrutinize lateral-directional stability at the preliminary design phase. Our work reveals the need for strong bare-airframe static directional stability to obtain favorable flying qualities
Convergent Close-Coupling Approach to Electron Impact Dissociation of the Polyatomic Molecule H 3 + and Its Isotopologues
No full textCross sections for electron impact dissociative excitation and ionization in scattering on vibrationally excited levels of the ground electronic state of H3+ and its isotopologues are reported in the energy range of 8 to 1000 eV. Calculations have been performed using a newly developed version of the molecular convergent close-coupling code. Cross sections for total dissociative excitation, ionization yielding atomic fragments such as D+, and the total inelastic cross section are presented. Good agreement with available experiments has been demonstrated
Application of synthetically trained three-dimensional U-Net to the detection of moving subpixel objects
No full textFuel Pump Power and Thermal Conceptual Design Investigation for a High Speed Vehicle
No full textThe design of a high-speed vehicle presents new challenges when compared to a lower speeds. At high speeds, there is no turbine or other rotating component within the propulsion system to generate electrical power, and or drive the fuel pump, necessitating an alternative means to turn the device to sustain thrust. As it is desirable to consider the power generation system earlier in the conceptual design process of high-speed vehicles, a means by which the power requirements of a generic geometry can be acquired quickly must be obtained, which for high speeds includes the power requirements of the fuel pump. In prior work, a conceptual design level 6DOF simulation was created to model the power and thermal requirements of high-speed vehicle subsystems. This work expands the previous work by implementing a fuel pump driven by an electric motor. The pump; modeled as a variable displacement pump, and motor are modeled and controlled in the developed SIMULINK model. A power and thermal analysis was performed for the entire subsystem and the profiles for each were extracted from the SIMULNK model. Upon simulation, both the power and thermal profiles for the fuel pump and motor subsystem were available for analysis at the conceptual design level