Search for a novel zero thermal expansion material: dilatometry of the AgI-CuI system

AgI is a well-known superionic conductor possessing a negative thermal expansion (NTE) coefficient while CuI is a p-type semiconductor possessing a positive thermal expansion coefficient. Pellets of X-Ray Diffraction (XRD) characterized compositions in the AgI–CuI system namely, β AgI, γ AgI, Ag_0.5Cu_0.5I, Ag_0.25Cu_0.75I, Ag_0.10Cu_0.90I, Ag_0.05Cu_0.95I and γ CuI have been examined by quartz pushrod dilatometry measurements in order to look for a zero thermal expansion material. It is found that the systematic displacement of Ag by Cu gradually reduces the NTE anomaly in AgI. The composition Ag_0.25Cu_0.75I apparently exhibits near-zero thermal expansion. The results are discussed qualitatively in terms of relevant models.     

Facile synthesis of reduced graphene oxide from Azadirachta indica for optical power limiting applications: an eco-friendly approach

Reduced graphene oxide (rGO) was synthesized successfully from dead leaves of neem trees using a novel synthesis method comprising combustion, washing, and drying. The synthesized carbonaceous material was subjected to systematic characterization analysis. The rGO material was subjected to X-ray powder diffraction analysis to determine the grain size and other structural parameters. The existence of defect and graphitic band was confirmed by FT-Raman analysis. The presence of a 2D band around 2700 cm^?1 indicated the formation of multi-layered graphene. SEM analysis was used to examine the structural morphology of the synthesized material. FTIR spectra revealed the information about the spectral properties of rGO. Compositional analysis revealed the presence of carbon and other contents in the specimen. The title material may be used in optical power limiters, according to z-scan and optical limiting analysis. The results indicate that the cost of synthesis would be significantly reduced when done on a large scale, using this procedure. Furthermore, rGO produced by this method is environmentally friendly, nontoxic and has a high yield.

     

Electrochemical behavior of two and one electron redox systems adsorbed on to micro- and mesoporous silicate materials: Influence of the channels and the cationic environment of the host materials

Electrochemical behavior of two electron redox system, phenosafranine (PS⁺) adsorbed on to micro- and mesoporous materials is investigated by cyclic voltammetry and differential pulse voltammetry using modified micro- and mesoporous host electrodes. Two redox peaks were observed when phenosafranine is adsorbed on the surface of microporous materials zeolite-Y and ZSM-5. However, only a single redox peak was observed in the modified electrode with phenosafranine encapsulated into the mesoporous material MCM-41 and when adsorbed on the external surface of silica. The observed redox peaks for the modified electrodes with zeolite-Y and ZSM-5 host are suggested to be primarily due to consecutive two electron processes. The peak separation ΔE and peak potential of phenosafranine adsorbed on zeolite-Y and ZSM-5 were found to be influenced by the pH of the electrolyte solution. The variation of the peak current in the cyclic voltammogram and differential pulse voltammetry with scan rate shows that electrodic processes are controlled by the nature of the surface of the host material. The heterogeneous electron transfer rate constants for phenosafranine adsorbed on to micro- and mesoporous materials were calculated using the Laviron model. Higher rate constant observed for the dye encapsulated into the MCM-41 indicates that the one-dimensional channel of the mesoporous material provides a more facile micro-environment for phenosafranine for the electron transfer reaction as compared to the microporous silicate materials. The stability of the modified electrode surface was investigated by multisweep cyclic voltammetry.     

BLSBA‐ED‐SSO: Bivariate Lévy‐stable bat algorithm‐based energy detection for spectrum sensing optimization in cognitive radio networks (CRNs)

The vacant licensed spectrum can be employed by the secondary users in cognitive radio networks. Nevertheless, this process of identification is frequently agreed with shadowing, multipath fading and receiver uncertainty problems. The primary contributions of the spectrum sensing techniques adopted in this work mainly concentrate on energy detection for spectrum sensing as well as to recognize the optimal spectral estimation according to the multitaper spectral estimation. The algorithm proposed in this work is based on bivariate Lévy‐stable bat algorithm (BLSBA), energy detector (ED), and with the help of K out of M fusion rule; it is analysed for the single user as well as cooperative multiple users. In the BLSBA algorithm, a modified search equation with more helpful information from the search experiences is brought‐in to create an optimal energy solution and bivariate Lévy‐stable random walk is associated with BLSBA to remove the trapping process into local optima. The energy detection is defined numerically from this optimal detection. At last, a multi‐taper spectral estimator (MSE) is proposed to cognitive radio detection for a huge network. The simulation results in both cases are computed and checked with the help of a BLSBA optimizer. For an individual secondary user scenario, the advancement of MSE to the ED is broadly described. Experimental result indicates that the objective false alarm likelihood is minimized and the demanded signal‐to‐noise ratio is accomplished to the extent.     

Statistical adaptive sensing by detectors with spectrally overlapping bands

It has recently been reported that by using a spectral-tuning algorithm, the photocurrents of multiple detectors with spectrally overlapping responsivities can be optimally combined to synthesize, within certain limits, the response of a detector with an arbitrary responsivity. However, it is known that the presence of noise in the photocurrent can degrade the performance of this algorithm significantly, depending on the choice of the responsivity spectrum to be synthesized. We generalize this algorithm to accommodate noise. The results are applied to quantum-dot mid-infrared detectors with bias-dependent spectral responses. Simulation and experiment are used to show the ability of the algorithm to reduce the adverse effect of noise on its spectral-tuning capability.     

Engineering On‐Surface Spin Crossover: Spin‐State Switching in a Self‐Assembled Film of Vacuum‐Sublimable Functional Molecule

The realization of spin‐crossover (SCO)‐based applications requires study of the spin‐state switching characteristics of SCO complex molecules within nanostructured environments, especially on surfaces. Except for a very few cases, the SCO of a surface‐bound thin molecular film is either quenched or heavily altered due to: (i) molecule–surface interactions and (ii) differing intermolecular interactions in films relative to the bulk. By fabricating SCO complexes on a weakly interacting surface, the interfacial quenching problem is tackled. However, engineering intermolecular interactions in thin SCO active films is rather difficult. Here, a molecular self‐assembly strategy is proposed to fabricate thin spin‐switchable surface‐bound films with programmable intermolecular interactions. Molecular engineering of the parent complex system [Fe(H₂B(pz)₂)₂(bpy)] (pz = pyrazole, bpy = 2,2′‐bipyridine) with a dodecyl (C₁₂) alkyl chain yields a classical amphiphile‐like functional and vacuum‐sublimable charge‐neutral Fe^II complex, [Fe(H₂B(pz)₂)₂(C₁₂‐bpy)] (C₁₂‐bpy = dodecyl[2,2′‐bipyridine]‐5‐carboxylate). Both the bulk powder and 10 nm thin films sublimed onto either quartz glass or SiO_x surfaces of the complex show comparable spin‐state switching characteristics mediated by similar lamellar bilayer like self‐assembly/molecular interactions. This unprecedented observation augurs well for the development of SCO‐based applications, especially in molecular spintronics.     

Sorption of Cu(II) ions by nano‐scale zero valent iron supported on rubber seed shell

This study focused on synthesising nano‐scale zero valent iron (NZVI) impregnated on a low‐cost agro‐waste material, rubber seed shell (RSS), by borohydride reduction method. The characterisation studies of NZVI‐RSS were performed by Fourier transform infrared spectroscopy, scanning electron microscopy and X‐ray diffraction. The adsorption execution of NZVI‐RSS for Cu(II) ions evacuation from synthetic wastewater was explored by batch studies. The optimum condition for the present adsorption system is as follows: Cu(II) ion concentration = 25 mg/l; solution pH = 6.0; contact time = 30 min; NZVI‐RSS dose = 3 g/l; temperature = 30°C. The sorption data were best portrayed by pseudo‐first‐order and Freundlich models. The outcomes demonstrated the multilayer sorption of Cu(II) ions by NZVI‐RSS. The Langmuir capacity was observed as 48.18 mg/g. Thermodynamic parameters, ΔG °, ΔH ° and ΔS ° were ascertained, and it was watched that the adsorption system was unconstrained and exothermic. The sticking probability for Cu(II) ions by NZVI‐RSS was found to be high at lower temperature. At long last, the research inquire about reasoned that NZVI‐RSS has demonstrated unrivalled adsorption capacity. Also NZVI‐RSS is thought to be really green and financially amicable support for wastewater treatment.Inspec keywords: adsorption, copper, X‐ray diffraction, scanning electron microscopy, wastewater treatment, Fourier transform infrared spectroscopyOther keywords: nano‐scale zero valent iron, rubber seed shell, copper ions, borohydride reduction method, NZVI‐RSS, Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, adsorption execution, synthetic wastewater, Langmuir capacity, Freundlich models, adsorption system, wastewater treatment, adsorption capacity, Cu     

Relationship between process parameters and mechanical properties of friction stir processed AA6063-T6 aluminum alloy

In this investigation the surfaces of AA6063-T6 aluminum alloy were friction sir processed and the effects of process variables such as axial force, tool feed and rotational speed were studied. For certain combinations of the process variables, a maximum increase of 46.5% in the ultimate tensile strength, 133% in ductility and 33.4% in microhardness in relation to the parent material was observed. The microstructural observations revealed a defects constrained structure under an axial force of 10 kN. In addition, a mathematical model was developed to establish the relationship between the different process variables and their mechanical properties. The established model was validated through further experiments. The deviation between the developed model and experiments was within 9% for the process variables yield, tensile strengths and Vickers microhardness and for ductility, it was around 12%.     

Holographic grating studies in pendant xanthene dyes containing poly(alkyloxymethacrylate)s

A series of xanthene dyes based poly(alkyloxymethacrylate)s were synthesized with even number of side-chain methylene spacers by free radical addition polymerization method for holographic grating studies. Chemical structure of monomers and polymers were confirmed by FTIR and ¹H-NMR spectroscopy. Thermal property was investigated by TGA and DSC. Lengthy spacers favor improved optical quality film formation than shorter spacer length containing polymers; however, thermal stability and Tm decreased. Absorption and emission spectra have been studied in different polar solvents. UV–vis absorption maxima were broad and red-shifted with increasing spacer length. Life-time decay analysis exhibited double exponential decay. Polymer films were tested for holographic grating formation and their diffraction efficiency compared. Photo bleaching mechanism of polymer films was disclosed by measuring electrochemical potential value.