Technique for measuring the beam shape of pulsed lasers

A simple technique for the measurement of the beam shape parameters of pulsed lasers, with just a single pulse of the laser is described. It involves the use of several beam dividers inclined at very small angles to the beam axis, reflecting the beam back to a screen or a phosphor placed near the exit of the laser. The reflected images are then photographed by a camera to yield the beam parameters.     

Incorporating quantitative reliability engineering measures into tradespace exploration

Recently, tradespace analysis and exploration has emerged as an important focus area within the Department of Defense Engineered Resilient System initiative, which draws upon engineering concepts, science, and design tools to produce trusted and effective solutions for a wide range of operational contexts. Most of the previous research on tradespace analysis, including those developed for rotorcraft, emphasize performance. However, non-functional requirements such as reliability, availability, and maintainability have received minimal consideration, despite their direct influence on program level concerns such as operation and support as well as affordability. This paper proposes a strategy to incorporate reliability engineering into tradespace analysis. We also develop a subsystem-level reliability investment model that is illustrated through a simplified example. Our results suggest that reliability investment could achieve significant savings over a systems lifecycle, thereby enabling improved fleet availability and a larger fleet size.     

A low‐cost high‐gain dual polarized antenna design from cuboids and shorting strips for base stations

This article presents a novel low‐cost high‐gain dual‐polarized antenna using suspended cuboid and ground connected cuboid geometry. The design structure of the antenna is simple and it's all components are fabricated by a copper sheet of thickness 0.5 mm. The prototype is fabricated and measured and has ?15 dB impedance bandwidths of 33.33%(2.5‐3.5 GHz) with broadside gain of 9.2 ± 0.3 dBi and 32.25%(2.6‐3.6 GHz) with broadside gain 9 ± 0.3 dBi over bandwidths when measured from port 1 and port 2, respectively. The isolation between the ports is enhanced by shorting suspended cuboid from the ground plane and measured one more than 17 dB from 2.45 to 3.7 GHz. The proposed dual polarized antenna can be used for base stations such as Wireless Local Area Network (WLAN), Long Term Evolution (LTE), and Worldwide Interoperability for Microwave Access (WiMAX) applications. The antenna is designed and simulated and there are good agreements between simulated and measured results are obtained.     

Zone-wise investigation of creep behaviour 9Cr–1Mo steel weld joints

Distinct regions such as weld metal, heat-affected zone (HAZ) and base metal of P9 steel weld joints fabricated by various welding processes were investigated using impression creep testing. Smaller prior austenitic grain size, lower density of precipitates and dislocations resulted in faster recovery and higher creep rate of HAZ in comparison to the weld and base metal. Compared to base metal, shielded metal arc weld (SMAW) and activated tungsten inert gas (A-TIG) weld of the P9 steel weld joints exhibited better resistance to creep and displayed higher activation energy due to their coarser prior austenite grain size. A-TIG HAZ exhibited superior creep properties compared to the SMAW and TIG HAZ due to the presence of higher number density of precipitates.     

Studying the resistivity imaging of chicken tissue phantoms with different current patterns in Electrical Impedance Tomography (EIT)

A current injection pattern in Electrical Impedance Tomography (EIT) has its own current distribution profile within the domain under test. Hence, different current patterns have different sensitivity, spatial resolution and distinguishability. Image reconstruction studies with practical phantoms are essential to assess the performance of EIT systems for their validation, calibration and comparison purposes. Impedance imaging of real tissue phantoms with different current injection methods is also essential for better assessment of the biomedical EIT systems. Chicken tissue paste phantoms and chicken tissue block phantoms are developed and the resistivity image reconstruction is studied with different current injection methods. A 16-electrode array is placed inside the phantom tank and the tank is filled with chicken muscle tissue paste or chicken tissue blocks as the background mediums. Chicken fat tissue, chicken bone, air hole and nylon cylinders are used as the inhomogeneity to obtained different phantom configurations. A low magnitude low frequency constant sinusoidal current is injected at the phantom boundary with opposite and neighboring current patterns and the boundary potentials are measured. Resistivity images are reconstructed from the boundary data using EIDORS and the reconstructed images are analyzed with the contrast parameters calculated from their elemental resistivity profiles. Results show that the resistivity profiles of all the phantom domains are successfully reconstructed with a proper background resistivity and high inhomogeneity resistivity for both the current injection methods. Reconstructed images show that, for all the chicken tissue phantoms, the inhomogeneities are suitably reconstructed with both the current injection protocols though the chicken tissue block phantom and opposite method are found more suitable. It is observed that the boundary potentials of the chicken tissue block phantoms are higher than the chicken tissue paste phantom. SNR of the chicken tissue block phantoms are found comparatively more and hence the chicken tissue block phantom is found more suitable for its lower noise performance. The background noise is found less in opposite method for all the phantom configurations which yields the better resistivity images with high PCR and COC and proper IR_Mean and IR_Max neighboring method showed higher noise level for both the chicken tissue paste phantoms and chicken tissue block phantoms with all the inhomogeneities. Opposite method is found more suitable for both the chicken tissue phantoms, and also, chicken tissue block phantoms are found more suitable compared to the chicken tissue paste phantom.     

Efficient piezoelectric ZnO nanogenerators based on Au-coated silica sphere array electrode

We reported ZnO nanorod-based piezoelectric nanogenerators (NGs) with Au-coated silica sphere array as an efficient top electrode. This electrode can readily bend the ZnO nanorods due to its enhanced surface roughness, thus resulting in more increased and regular piezoelectric charge output. Under a low external pushing force of 0.3 kgf, the output current and voltage were increased by approximately 2.01 and 1.51 times, respectively, in comparison with a conventional Au top electrode without silica spheres. Also, the effect of Au-coated silica spheres on the bending radius of ZnO nanorods was theoretically investigated.     

Thermal gap conductance at low contact pressures (<1 MPa): Effect of gold plating and plating thickness

Thermal contact conductance (TCC) measurements are made on bare and gold plated (?0.5 μm) oxygen free high conductivity (OFHC) Cu and brass contacts in vacuum, nitrogen, and argon environments. It is observed that the TCC in gaseous environment is significantly higher than that in vacuum due to the enhanced thermal gap conductance. It is found that for a given contact load and gas pressure, the thermal gap conductance for bare OFHC Cu contacts is higher than that for gold plated contacts. It is due to the difference in the molecular weights of copper and gold, which influences the exchange of kinetic energy between the gas molecules and contact surfaces. Furthermore, the gap conductance is found to increase with increasing thickness of gold plating. Topography measurements and scanning electron microscopy (SEM) analysis of contact surfaces revealed that surfaces become smoother with increasing gold plating thickness, thus resulting in smaller gaps and consequently higher gap conductance.     

Synthesis and characterization of silver molybdate nanowires, nanorods and multipods

Silver molybdate nanowires, nanorods and multipods like structures have been prepared by an organic free hydrothermal process using ammonium molybdate and silver nitrate solutions. The powder X-ray diffraction (PXRD) patterns reveal that the silver molybdate belongs to anorthic structure. The thickness, 200–500 nm, for silver molybdate nanorods/wires and 2–5 μm for microrods are identified from SEM images. UV-visible spectrum of silver molybdate nanorods/nanowires shows maximum absorbance at 408 nm. Photo-luminescence (PL) spectrum exhibits UV emission at 335 nm, violet emission at 408 nm and a weak green emission at 540 nm. The influence of hydrothermal synthesis conditions on silver molybdate nanowires, nanorods and multipods compositions were established.     

Glycerol Hydrogenolysis to 1,2-Propanediol by Cu/ZnO/Al2O3 Catalysts

The effect of preparation methods on the Cu/ZnO/Al₂O₃ catalyst structure and catalytic activity on liquid glycerol hydrogenolysis to 1,2-propanediol has been investigated. The physicochemical properties of the catalysts were characterized by BET, XRD, TG/DTA, NH₃-TPD and TPR. The experimental results showed that the catalyst prepared by an oxalate gel–coprecipitation had the highest activity. At 200 °C and 400 psi hydrogen pressure, the glycerol conversion and 1,2-propanediol selectivity catalyzed by the Cu/ZnO/Al₂O₃ catalyst prepared via oxalate gel–coprecipitation were 92.3 and 94.5 % respectively. It was found that the 1,2-propanediol selectivity was dependent on hydrogen pressure and the un-desired by-products were mainly due to the side reactions caused by the presence of the intermediate acetol.     

Investigating the magnetohydrodynamic flow of a couple stress dusty fluid along a stretching sheet in the presence of viscous dissipation and suction

A computational study for investigating the flow and heat transfer phenomena in the unsteady magnetohydrodynamic couple stress dusty fluid flow over a linearly stretching porous surface in the presence of viscous dissipation effects is presented. The governing equations, in nondimensional form, are tackled by the exploitation of the standard spectral quasi-linearization methodology. The estimations of flow rate and temperature profiles are pictured diagrammatically. In contrast, the local skin friction and heat transfer rates are placed in tabular form for various values of thermofluidic parameters. The numerical results of a current investigation are compared with previously available results and located to be sensible agreement as shown in Tables 1 and 2. It is analyzed that by elevating the specific heat parameter and couple stress parameter, the temperature profile and the resulting thickness of the boundary layer are depressed. In comparison, an increase in thermal boundary layer thickness and a decrease in thickness of the momentum boundary layer were found with the rising magnetic parameter values.