Effect of Initial Grain Size on Friction Stir Weldability for Rolled and Cast CoCrFeMnNi High-Entropy Alloys

Metals and Materials International - This study investigated the influence of the initial grain size on the plastic deformation and tunnel defects that occurred from friction stir welding of...     

Systematic robustness analysis of least squares mobile robot velocity estimation using a regular polygonal optical mouse array

This paper presents the robust velocity estimation of an omnidirectional mobile robot using a regular polygonal array of optical mice that are installed at the bottom of a mobile robot. First, the velocity kinematics from a mobile robot to an array of optical mice is derived, from which the least squares estimation of the mobile robot velocity is obtained as the simple average of the optical mouse velocity readings. Second, it is shown that a redundant number of optical mice contributes to the robustness of the least squares mobile robot velocity estimation against both measurement noises and partial malfunction of optical mice. Third, the sensitivity analysis of the least squares mobile robot velocity estimation to imprecise installation of optical mice is made, from which a practical method of optical mouse position calibration is devised. Finally, some experimental results using commercial optical mice are given to demonstrate the validity and performance of the proposed mobile robot velocity estimation. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Detailed assessment of mesh sensitivity for CFD simulation of coal combustion in a tangential-firing boiler

Journal of Mechanical Science and Technology - Computational fluid dynamics (CFD) has become an essential tool for optimizing the design and diagnosing the operation of a boiler. However, the...     

Optimally overlapped ultrasonic sensor ring design for minimal positional uncertainty in obstacle detection

This paper presents the optimal overlapping arrangement of a circular array of ultrasonic sensors for minimal positional uncertainty in obstacle detection. First, it is shown that beam overlap among three adjacent ultrasonic sensors leads to significant reduction of positional uncertainty. Second, the positional uncertainty of an overlapped ultrasonic sensor ring is compared to a single ultrasonic sensor in terms of a collision-free region with obstacles. Third, the optimal design index for an overlapped ultrasonic sensor ring is defined as the area closest between the non-overlapped and overlapped sensing sub-zones. Fourth, using commercial low directivity ultrasonic sensors, an optimally overlapped ultrasonic sensor ring is given along with its prototype installed on top of a mobile robot. Finally, experimental results are given to demonstrate the validity and performance of our overlapped ultrasonic sensor ring prototype.     

Tensile and Microstructural Characteristics of Fe-24Mn Steel Welds for Cryogenic Applications

Metals and Materials International - Herein, we investigated the weldability and relationship between microstructure and tensile properties in 24 wt% Mn steel welds and, specifically,...     

Enhancement in light extraction efficiency of organic light emitting diodes using double-layered transparent conducting oxide structure

We examined double-layered transparent conducting oxide (TCO) anode structures consisted of zinc-doped indium oxide (IZO) over the gallium-doped zinc oxide (GZO), and IZO over the GZO with electrochemical treatment. In bottom type OLEDs, power efficiency and current efficiency were enhanced by a factor of 1.50 and 1.14 at a current density of 10 mA/cm² in IZO/GZO anode structure, compared to the only IZO anode structure. Due to the reduced sheet resistance of the IZO/GZO TCO surface, the operating voltage of the OLED with IZO/GZO anode structure was lowered, leading to mostly enhance power efficiency. More enhanced in power efficiency and current efficiency by a factor of 1.21 and 1.25 at a current density of 10 mA/cm² were achieved in IZO/GZO anode structure with electrochemical treatment, compared to the IZO/GZO anode structure due to the change of the surface morphology of the GZO and the existence of the nanoporous layer beneath the GZO surface by an electrochemical treatment. In total, double-layered IZO/GZO anode structure with electrochemical treatment was revealed at an enhancement factor of 1.80 in power efficiency and 1.42 in current efficiency, compared to the only IZO anode structure.     

A Topologically Distinct Modified Peptide with Multiple Bicyclic Core Motifs Expands the Diversity of Microviridin-Like Peptides

Microviridins are ribosomally synthesized and post-translationally modified peptides (RiPPs) that contain multiple intramolecular ω-ester or ω-amide crosslinks between two side chains in peptides. This type of the side-to-side macrocyclization may generate diverse structures with distinct topology and ring sizes, but the majority of the microviridin-like RiPPs present only a single consensus sequence with a tricyclic architecture. Here, we expanded the natural diversity of the microviridin-like modified peptides by determining the crosslinking connectivity of a new modified peptide, mTgnA and its homologous RiPPs, which we named the thuringinin group. Members of the thuringinin group have core motifs with a distinct consensus sequence, which is transformed to a novel hairpin-like bicyclic structure by the cognate ATP-grasp enzyme. We suggest that the microviridin-like RiPPs naturally have novel sequences and architectures beyond those found in microviridins and comprise a larger RiPP family, termed omega-ester containing peptides (OEPs).     

Effect of post weld heat treatment on weldability of high entropy alloy welds

The effect of post weld heat treatment (PWHT) temperature on laser beam welds in high-entropy alloys (HEAs) using a cold-rolled cantor system (CoCrFeMnNi) was investigated. Laser welding of low heat input was applied to reduce thermal distortion. The cold-rolled HEA welds indicated larger grain size and inferior tensile/hardness properties as compared to the base metal (BM). By applying PWHT, the welds showed superior hardness to the BM with no variation in the face-centred cubic phase and a decrease in the size and fraction of CrMn oxide inclusions. As the PWHT temperature increased (800–1000°C), the variation in the grain size decreased between the weld metal and heat-affected zone, thus resulting in approximately the same tensile strength and elongation of the transverse welds as compared to the BM.     

Optimal placement of optical mice for accurate mobile robot velocity estimation

There can be some restrictions during the installation of optical mice at the bottom of a mobile robot, owing to the non-circular base or other existing structures of the robot. This paper presents the optimal placement of optical mice under positional restriction during installation for the velocity estimation of a mobile robot. First, the velocity kinematics between a mobile robot and an array of two or more optical mice is derived, mapping the velocity of a mobile robot in the world coordinate frame to the velocities of optical mice in their local frames. Second, the error characteristics of the velocity estimation of a mobile robot are represented by the uncertainty ellipsoid, and the performance index is then defined as the inverse of the volume of the ellipsoid, which should be minimized for the optimal placement of optical mice. Third, the global optimization strategy is stated in terms of the distances to each optical mouse and the geometrical center of all optical mice, and the local optimization strategy is described as the positional change of each optical mouse, leading to optimal optical mouse placement. Fourth, simulation results for three optical mice within a given elliptical region are given to show how the positional restriction during installation affects the resulting optimal optical mouse placement.     

Crystallographic texture in pulsed laser deposited hydroxyapatite bioceramic coatings

The orientation texture of pulsed laser deposited hydroxyapatite coatings was studied by X-ray diffraction techniques. Increasing the laser energy density of the KrF excimer laser used in the deposition process from 5 to 7 J/cm(2) increases the tendency for the c-axes of the hydroxyapatite grains to be aligned perpendicular to the substrate. This preferred orientation is most pronounced when the incidence direction of the plume is normal to the substrate. Orientation texture of the hydroxyapatite grains in the coatings is associated with the highly directional and energetic nature of the ablation plume. Anisotropic stresses, transport of hydroxyl groups and dehydroxylation effects during deposition all seem to play important roles in the texture development.