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Ultra-Low-Temperature CO Oxidation Activity of Octahedral Site Cobalt Species in Co3O4 Based Catalysts: Unravelling the Origin of the Unique Catalytic Property
No full textCo3O4 with spinel structure shows CO oxidation activity at very low temperature under dry conditions. This study aims at finding the origin of the unique catalytic activity of Co species in Co3O4 based oxides. Although, octahedral site Co3+ species have been reported to be active in Co3O4 based catalysts, there is no solid explanation as to why Co is so special as compared with other metals like Fe having similar redox states. In this study, mainly, three model spinel catalysts including MnCo2O4, MnFe2O4, and CoCr2O4 have been chosen. A detailed analysis of bulk and crystal surface structure, surface properties of the catalysts, and redox properties of the active metals has been performed to understand the unusual catalytic activity. Low-temperature CO oxidation activity decreases in the following order: MnCo2O4 ≫ MnFe2O4 > CoCr2O4. It indicates that the Co2+ species in a tetrahedral site (in CoCr2O4) remains inactive for low-temperature catalytic activity, while Co3+ in an octahedral site (in MnCo2O4) is active in Co3O4 based catalysts. This result is corroborated with CoFe2O4 which shows a higher activity than CoCr2O4, as it has partial occupation of the octahedral site. Fe, being a weak redox metal, does not show low-temperature activity, although crystallite facets of MnCo2O4 and MnFe2O4 catalysts are predominantly exposed in the (100) and (110) lattice planes, which contain quite similar concentrations of Co3+ and Fe3+ species in both. The intensity of the redox peak for CO oxidation involving a Co3+/Co2+ couple in MnCo2O4 indicates a highly favorable reaction, while a nonresponsive behavior of Co species is observed in CoCr2O4. As expected, MnFe2O4 is proven to be weak, giving a much lower intensity of electrochemical CO oxidation. Both CO- and H2-TPR indicate a much higher reducibility of Co species in MnCo2O4 as compared with Co species in CoCr2O4 or Fe in MnFe2O4
EEG as a tool to measure cognitive load while playing Sudoku: A preliminary study
Get PDFCognitive load or mental workload in human beings is an important parameter associated with the task being performed. The level of task and the learning curve for any task has a certain cognitive load or mental workload. Apart from causing stress and mental exhaustion, increase in cognitive load beyond a critical limit may affect the performance on the end task. There is a need to explore noninvasive and non- intrusive physiological means of measuring cognitive load to identify the subjective performance and well been. This paper discusses identification of EEG as one of the means, identification of suitable EEG frequency bands and spatial locations to assess the cognitive load based on available literature and also to demonstrate measured load based on an experimental study performed using a commonly played Sudoku game
Inertial Angle of Attack estimation for a small transport aircraft
No full textIn this work, warning flights of a small commuter aircraft are analyzed. One of the reasons for warning to occur in Stall Warning System (SWS) is due to difference in Alpha/ Angle of Attack (AOA) values computed using two methods exceeds ± 5°. In the first method, vane sensors are used to acquire local alpha and get freestream AOA using airdata calibration tables. Whereas, inertial alpha is computed using inertial sensor measurements from Attitude and Heading Reference Unit (AHRS) and Air Data Computer Unit (ADCU). The flights that are investigated in this work are those where, the alerts happened because of this reason. Cause for the discrepancy is clearly presented. Solution to the problem has been proposed using recursive filtering technique. An Extended Kalman Filter (EKF) based flight path reconstruction technique (FPR) is used to estimate true AOA and inertial AOA. Flight data is analyzed offline and results are presented for the same
Application of Generic Flight Controller Design Approach for A Delta Canard Fighter AircraftADMIRE
No full textThis paper presents the application of the recently developed Generic Flight Controller design approach by the authors for a delta canard fighter aircraft referred to Aero Data Model in Research Environment (ADMIRE). The generic flight controller developed for high performance fixed wing aircrafts uses the good features of nonlinear dynamic inversion with time scale separation, control allocation and integrator backstepping with the major advantage that the whole design cycle can be carried out quickly. The results obtained for ADMIRE using generic flight controller results have been compared with those obtained from the ADMIRE controller taken from literature. The quick adoption of generic flight controller to ADMIRE has been demonstrated along with encouraging results
Optimization of W/WAlSiN/SiON/SiO2 tandem absorber consisting of double layer anti-reflection coating with broadband absorption in the solar spectrum region
No full textA novel spectrally selective tandem stack of W/WAlSiN/SiON/SiO2 was deposited on stainless steel 304 and silicon substrates using a four-cathode reactive unbalanced magnetron sputtering system. The coatings were deposited by sputtering of W, Al and Si targets in Ar, Ar + N2, Ar + N2 + O2, and Ar + O2 plasmas. The process parameters were optimized by studying the optical properties of the individual layers using UV-VIS-NIR spectrophotometer and Fourier transform infrared spectroscopy measurements. The high spectral selectivity of the tandem stack was achieved by varying the reactive gas flow rates of N2 and O2 and thickness of individual layers. In the tandem stack, W layer acts as an IR reflector, WAlSiN acts as the main absorber layer, SiON, and SiO2 layers act as anti-reflecting layers. The tandem stack was designed based on graded refractive indices of individual layers with a double layer anti-reflection coating. The tandem stack exhibits superior spectral selectivity with a high solar absorptance of 0.955 in the broadband solar spectrum region and low thermal emissivity of 0.10 in the infrared region. The coating was found to be thermally stable up to 600 °C in vacuum for 200 h under cycling heating conditions
Technological aspects of microbial fuel cells and soil based green energy conversion system
No full textThis paper presents technological aspects, operating principle, and scientific applications of the microbial fuel cell (MFC). The MFC is a technology for the extraction of clean energy from biomass such as organic wastes; hence, comes under Green Energy Conversion System (GECS). The cell uses bacteria as biocatalysts to generate electricity by digesting biodegradable organics present in the organic waste material, through a catalytic reaction of microorganisms under an anaerobic condition. MFC has received considerable attention to offering the possibility of biological waste treatment and energy production simultaneous. Only in a few biosensors, the MFC is used practically, providing current for low power devices. Some researchers are uncovering that the importance of MFC technology is not only the production of electricity but the ability of electrode associated microbes to degrade wastes and toxic chemicals. This paper provides a platform to explore the possibilities of generating renewable power using biomass and the working principle of MFC technology with its applications like biological oxygen demand sensing, wastewater treatment, etc. Therefore, the paper has suggested the methods for electricity generation using a soil based MFC and water extraction from grass clippings using MFC. The experimental results showed better results than the previous research works
Low-cycle fatigue of IN 718: Effect of waveform
No full textThe influence of various strain waveforms on the low-cycle fatigue of IN 718 tested at
650°C has been investigated. The straining paths are accompanied by dwell-induced creep component(s) or unequal strain distribution in different portions of cycles reducing strength of material. The investigation intends to clarify mainly mechanistic aspects of relaxation-fatigue interaction. Features of time-dependent effect induced by nonpeak dwell and the same accompanied by peak dwell, slow unloading from the peak to a lower strain, and different loading and unloading rates are compared in terms of stress amplitude responses, mean stress relaxation, hysteresis loops, life, and damage parameter DC-F. Softening is common in all the cases, and degree of softening varies linearly with life. The energy-based life prediction model has been found to work well for the data, and we have introduced energy fraction–based approach to observe simultaneous contribution from both creep and fatigue on life
A comparative numerical study of standard 3D composite plate using virtual crack closure technique and cohesive zone modelling method
No full textA standard square plate specimen made up of Carbon Fibre Reinforced Polymer (CFRP) and Glass Fibre Reinforced Polymer (GFRP) laminates with an artificially-introduced delamination was considered for evaluation of fracture parameters using Abaqus-Standard software. Though there are several methods to evaluate the initiation of delamination using software, Virtual Crack Closure Technique (VCCT) and Cohesive Zone Modelling (CZM) method are commonly used. By using the above-mentioned methods, the Quasi-Isotropic (QI) composite laminates were analysed for varying compressive loads. The Load-Displacement responses were reported and seen to be in overall good statement with each other, while the modelling effort and computational time required were quite higher in CZM method compared to VCCT. Onset of delamination growth for CFRP and GFRP laminates was studied using VCCT by evaluating Strain Energy Release Rates (SERR). The results for both the specimens were compared and reported
Frequency domain approach for probabilistic flutter analysis using stochastic finite elements
No full textIn this work, a stochastic finite element method based on first order perturbation approach is developed for the probabilistic flutter analysis of aircraft wing in frequency domain. Here, both bending and torsional stiffness parameters of the wing are treated as Gaussian random fields and represented by a truncated Karhunen–Loeve expansion. The aerodynamic load on the wing is modeled using Theodorsen’s unsteady aerodynamics based strip theory. In this approach, Theodorsen’s function, which is a complex function of reduced frequency, is also treated as a random field. The applicability of the present method is demonstrated by studying the probabilistic flutter of cantilever wing with stiffness uncertainties. The present method is also validated by comparing results with Monte Carlo simulation (MCS). From the analysis, it is observed that torsional stiffness uncertainty has significant effect on the damping ratio and frequency of the flutter mode as compared to bending stiffness uncertainty. The probability density functions of damping ratio and frequency using perturbation technique and MCS are also discussed at various free stream velocities due to stiffness uncertainties. Furthermore, the flutter probability of the cantilever wing is studied by defining implicit limit state function in conditional sense on flow velocity for the flutter mode. Both perturbation and MCS are considered to study the flutter probability of the wing. From the cumulative distribution functions of flutter velocity, it is noticed that the presence of uncertainty in torsional rigidity lowers the predicted flutter velocity in comparison to uncertainty in bending rigidity
Modes of base pressure fluctuations: Shape, nature, and origin
No full textAn experimental study was carried out to examine the unsteady pressure field on the base of a cylindrical afterbody at freestream Mach numbers ranging from high subsonic to low supersonic speeds. The objective was to gain insights into spatial modes of base pressure fluctuations by identifying their shape and nature, and the mechanism of their origin using spectral proper orthogonal decomposition. It is observed that 90–95% of the cumulative energy content
resides within the first three modes at all Strouhal numbers for all freestream Mach numbers. Further, at subsonic Mach numbers and for Strouhal numbers O�10−2, the shape of the modes indicates that their nature is symmetric, and the mechanism for the origin of the dominant mode is the pulsing action of the recirculation bubble. However, for Strouhal numbers O�10−1, the shape of the modes is asymmetric, indicating that their nature is antisymmetric, and the mechanism associated with the dominant mode is the radial displacement of the recirculation bubble coupled with
the motion of structures within the recirculation bubble. At supersonic Mach numbers and for all Strouhal numbers, the shape of the modes indicates that they are symmetric, and the dominant mechanism is the pulsing action of the
recirculation bubble