Reduction of sidelobe levels in multicarrier radar signals via the fusion of hill patterns and geometric progression

Multi-carrier waveforms have several advantages over single-carrier waveforms for radar communication. Employing multi-carrier complementary phase-coded (MCPC) waveforms in radar applications has recently attracted significant attention. MCPC radar signals take advantage of orthogonal frequency division multiplexing properties, and several authors have explored the use of MCPC signals and the difficulties associated with their implementation. The sidelobe level and peak-to-mean-envelope-power ratio (PMEPR) are the key issues that must be addressed to improve the performance of radar signals. We propose a scheme that applies pattern-based scaling and geometric progression methods to enhance sidelobe and PMEPR levels in MCPC radar signals. Numerical results demonstrate the improvement of sidelobe and PMEPR levels in the proposed scheme. Additionally, autocorrelations are obtained and analyzed by applying the proposed scheme in extensive simulation experiments.     

Structural Aspects of P2-Type Na0.67Mn0.6Ni0.2Li0.2O2 (MNL) Stabilization by Lithium Defects as a Cathode Material for Sodium-Ion Batteries

A known strategy for improving the properties of layered oxide electrodes in sodium-ion batteries is the partial substitution of transition metals by Li. Herein, the role of Li as a defect and its impact on sodium storage in P2-Na_0.67Mn_0.6Ni_0.2Li_0.2O₂ is discussed. In tandem with electrochemical studies, the electronic and atomic structure are studied using solid-state NMR, operando XRD, and density functional theory (DFT). For the as-synthesized material, Li is located in comparable amounts within the sodium and the transition metal oxide (TMO) layers. Desodiation leads to a redistribution of Li ions within the crystal lattice. During charging, Li ions from the Na layer first migrate to the TMO layer before reversing their course at low Na contents. There is little change in the lattice parameters during charging/discharging, indicating stabilization of the P2 structure. This leads to a solid-solution type storage mechanism (sloping voltage profile) and hence excellent cycle life with a capacity of 110 mAh g^-1 after 100 cycles. In contrast, the Li-free compositions Na_0.67Mn_0.6Ni_0.4O₂ and Na_0.67Mn_0.8Ni_0.2O₂ show phase transitions and a stair-case voltage profile. The capacity is found to originate from mainly Ni³⁺/Ni⁴⁺ and O^2-/O^2-δ redox processes by DFT, although a small contribution from Mn⁴⁺/Mn⁵⁺ to the capacity cannot be excluded.     

Adomian decomposition method for the MHD flow of a viscous fluid with the influence of dissipative heat energy

An investigation is carried out on the effect of dissipative heat energy on the flow of an electrically conducting viscous fluid past a shrinking sheet. Both viscous and Joule dissipation effects are considered along with heat generation/absorption for the enhancement of heat transfer properties. The governing nonlinear coupled partial differential equations are transformed into nonlinear ordinary differential equations by a suitable choice of similarity transformations. However, the complex transformed equations are solved by an approximate analytical method known as the Adomian decomposition method with a suitable initial guess solution assumed from the known initial conditions. Moreover, the behavior of several parameters characterizing the flow phenomena are studied via graphs and the numerical computations for the engineering coefficients are obtained and presented through tables. However, the major outcomes of the results are that a higher suction is required to resist the fluid temperature and sinks as well as the dissipative heat energy favors enhancing the fluid temperature at all points in the flow domain.     

Hypervariate constitutive modeling illustrated via aleatory uncertainty in a foundation model

Even if a ceramic's homogenized properties (such as anisotropically evolving stiffness) truly can be predicted from complete knowledge of sub-continuum morphology (e.g., locations, sizes, shapes, orientations, and roughness of trillions of crystals, dislocations, impurities, pores, inclusions, and/or cracks), the necessary calculations are untenably hypervariate. Non-productive (almost derailing) debates over shortcomings of various first-principles ceramics theories are avoided in this work by discussing numerical coarsening in the context of a pedagogically appealing buckling foundation model that requires only sophomore-level understanding of springs, buckling hinges, dashpots, etc. Bypassing pre-requisites in constitutive modeling, this work aims to help students to understand the difference between damage and plasticity while also gaining experience in Monte-Carlo numerical optimization via scale-bridging that reduces memory and processor burden by orders of magnitude while accurately preserving aleatory (finite-sampling) perturbations that are crucial to accurately predict bifurcations, such as ceramic fragmentation.     

Assessment of Mixture and Eulerian Multiphase Models in Predicting the Thermo-Fluidic Transport Characteristics for Fly Ash-Water Slurry Flow in Straight Horizontal Pipeline

The thermo-fluidic transport characteristics of the fly ash–water slurry flow in a straight horizontal pipe are predicted by deploying two different multiphase modeling strategies, viz. the mixture and the Eulerian multiphase models. Comparisons between the two model predictions in terms of the pressure drop and heat transfer coefficient are done along with the comparisons between the single (water) and the two phase system (slurry). Spherical fly ash particles, with diameter of 13 µm for an average inflow velocity ranging from 1 to 5 m/s and particle concentrations within 0–40% by volume for each velocity are considered as the dispersed phase carried by the carrier phase water. Significant differences between the two model predictions can be observed both from the qualitative and quantitative perspectives. This finally leads to the appropriate choice of the multiphase model for predicting the thermo-fluidic transport characteristics in slurry flow.     

3D MHD cross flow over an exponential stretching porous surface

The present study aims to investigate the effects of thermal‐diffusion and diffusion‐thermo onan magnetohydrodynamic convective flow of viscous fluids over an exponentially stretching sheet. Thermal radiation effects are also considered in the study. This analysis is carried out in three dimensions and a similarity transformation is adopted to get a set of ordinary differential equations from a set of partial differential equations. And the Fourth‐order Runge‐Kutta method and shooting technique along with the secant method are employed to find out an iterative solution. We also analyze here the influence of the variable magnetic field, nonuniform permeability and variable chemical reaction on the fluid flow. The impact of various pertinent parameters of interest has extensively been explored through graphs and tables. The major findings of the present study are that resistive Lorentz force diminishes the fluid velocity and uplifts the thermal as well as concentration fields. Inclusion of porous matrix improves the viscous drag force which in turn augments wall shear stresses and peters out the heat and mass transfer rates from the sheet. In addition, the thermal expansion coefficient has an inverse relation with temperature.     

Lab scale optimization of various factors for photocatalytic hydrogen generation over low cost Cu0.02Ti0.98O2-δ photocatalyst under UV/Visible irradiation and sunlight

We have demonstrated earlier that maximum H₂ generated @ 1.167 l/h/m² over Cu_0.02Ti_0.98O_2-δ photocatalyst with apparent quantum efficiency, AQE of 7.5% and solar fuel efficiency, SFE of 3.9% under sunlight. With an aim to scale-up the solar photocatalytic hydrogen process to pilot plant, optimization studies at lab scale as well as in upscaled photoreactors were performed over Cu_0.02Ti_0.98O_2-δ, photocatalyst under UV/visible and sunlight. Cu_0.02Ti_0.98O_2-δ was synthesized by facile sol-gel route and characterized by relevant techniques. Several operational parameters were investigated in order to finalize the conditions which are most favourable for photocatalytic hydrogen yield. Factors such as photocatalyst loadings, v/v concentration of sacrificial reagent, replacement of methanol by industrial waste glycerol, role of different configuration of light source with reactor, effect of stirring during the photocatalytic reaction, effect of fluctuations of solar flux at hourly basis, illumination area on hydrogen yield were studied. Contribution of each factor in determining the hydrogen yield was quantified. Relative standard deviation in hydrogen yield as a function of each factor was estimated. Our findings suggest that in addition to catalyst loadings and sacrificial reagent, improved dispersion of photocatalyst obtained by stirring the reaction mixture in horizontal geometry resulted in enhanced H₂ yield. Hydrogen yield obtained at lab scale can be appropriately extrapolated with respect to illumination area instead of weight of photocatalyst. A relative standard deviation (RSD) of ± 3.82% and ± 4.53% in H₂ yield was calculated for sunny and cloudy days in time zone of 10.30–16.30 h IST. Deviation of H₂ yield was more on cloudy days and beyond 16:30 h. These studies have provided a daily window of 11:00–15:00 h to be utilized throughout the year for a commercial scaled up process, prohibiting the illumination during less productive hours of the day for shaping the improved economics of solar hydrogen generation. Our results obtained at lab scale would be useful to perform sunlight driven scaled –up photocatalytic process using low cost visible light efficient photocatalyst, Cu_0.02Ti_0.98O_2-δ.     

Electrochemical inspection of polypyrrole/chitosan/zinc oxide hybrid composites

Polymer nanocomposite composed of polypyrrole, chitosan, and zinc oxide nanoparticles has been synthesized and it has been evaluated for various electrochemical aspects of the current electrochemical industry. The polypyrrole (PPy) was synthesized by the chemical oxidative polymerization reaction by employing ammonium persulfate as oxidizing agent. Composites of polypyrrole/chitosan (PPy/Chy) and polypyrrole/chitosan/ZnO (PCZ) composites were synthesized by the solution blending method. Detailed structural, morphological, thermal characterization of PPy, PPy/Chy, and PCZ were performed to characterize the specific features of the systems. The composites exhibit better thermal stability and high surface area and the addition of ZnO nanoparticle increase the crystallinity of the composite. Electrochemical characterization of the ITO electrodes modified with PPy, PPy/Chy, and PCZ were performed using cyclic voltammetry, electrochemical impedance spectroscopy, and amperometry techniques. The present study highlights the role of a bio-compatible material with high surface area and conductive constituent for designing of various high performing electronic noninvasive sensors, biosensors, and so forth.