Influence of Different CH4/N2 Ratios on Structural and Mechanical Properties of a-CNx:H Film Synthesized Using Plasma Focus

Carbon nitride films were synthesized by operating the dense plasma focus device with different CH₄/N₂ admixture gas ratios and fixed 20 focus shots. The pressure and axial distance from anode tip were kept constant at 3 mbar and 8 cm respectively. Raman and X-ray photoelectron spectroscopy (XPS) techniques were used to observe the effect of CH₄/N₂ ratio on carbon nitride bonding. The XPS analysis showed that the terminating group C≡N is more dominant for the films synthesized using higher concentration of nitrogen which gives softer films. Field emission scanning electron microscopy results showed that the deposited films consist of nanoparticles and their agglomerates. The size of agglomerates increases with decreasing concentration of nitrogen in CH₄/N₂ admixture gas. Nanoindentation results showed the increase in hardness and elastic modulus values of films with decreasing concentration of nitrogen in CH₄/N₂ admixture gas. The hardness and elastic modulus values were found to be dependent on sp³ content in the film as well as the C≡N. The hardness and elastic modulus values of 10.7 and 229.8 GPa respectively were achieved for the films deposited with fixed 20 focus deposition shots and using CH₄/N₂ admixture gas ratio of 7:3.     

Magnetic Reynolds Number and Neon Current Sheet Structure in the Axial Phase of a Plasma Focus

The Magnetic Reynolds Number (MRN) in neon is computed as a function of Neon shock speed. The magnetic field profiles at various positions in the axial run down phase of the INTI Plasma Focus device are measured over a range of pressures from 2 to 20 Torr. These profiles are assessed for good electromagnetic coupling including measuring the current per unit current sheet thickness as a comparative measure of current sheet diffusion. It was found that at an axial current sheet speed of over 3.5 cm/μs (corresponding to MRN > 15), the current sheet has a compact profile with current density of 55 kA/cm of sheet thickness whereas at speeds below 2.8 cm/μs (corresponding to MRN < 10) the profile is more diffuse with current density less than 30 kA/cm of sheet thickness. Based on these studies it is proposed to take a speed of 3 cm/μs corresponding to an MRN of 10 as the minimum speed of neon current sheet below which the electromagnetic coupling begins to weaken.     

A publicly verifiable lossless watermarking scheme for copyright protection and ownership assertion

In this paper, a discrete cosine transform based copyright protection scheme that does not require the original image for logo verification is proposed. Features of logistic map and discrete cosine transform are used to generate the verification map. Digital signature and timestamp are used to make copyright proving publicly verifiable. We have combined cryptographic tools and digital watermarking, in order to enhance the security and reliability of copyright protection. In addition, chaotic map is used to generate a chaotic pattern image, which can be used as secret key to improve the security of proposed algorithm. Experiments are conducted to show the robustness and effectiveness of the proposed algorithm. Experimental results show that our scheme outperforms related works in most of the cases.     

Neural network applications in smart antenna arrays: A review

Techniques employed in the synthesis of antenna arrays vary from complex analytical methods to iterative numerical methods based on optimisation algorithms. The drawback of these techniques is that they usually consider the array factor but not the interaction between array elements and real-time problems. This omission induces an error in the resultant radiation pattern; therefore, the physical relations between the array feeding details and the corresponding radiation patterns are taken into account to improve the accuracy. The behaviour of an antenna array is nonlinear in nature, resulting in an extremely high complexity using this approach, and it is usually disregarded. A neural-network-based solution can avoid complexity by establishing a relation between the desired radiation patterns and feeding details such as voltage and spacing in the real antenna array and can help convert the real array into a smart array. Several neural network applications in smart antenna array synthesis are reviewed in this paper.     

Effect of arc current on microstructure,texturing and wear behavior of plasma sprayed CaZrO3 coatings

In order to enhance the biocompatibility of metallic implants, various ceramic coatings are currently in vogue. CaZrO₃, a promising candidate material, was deposited through plasma spraying on stainless steel (316L) substrates at arc currents of 400, 500 and 600 A. The coatings were characterized using a SEM, XRD, surface profilometers and a tribometer. It was found that the arc current had profound effects on the thickness, microstructure, phase evolution, crystallinity and wear behavior of the coatings. The cross-sectional images and fractographic analysis showed that a denser coating with better inter-splat fusion was produced at arc current of 600 A. The average roughness (Ra) of the coatings increased from 3.62 to 6.68 μm as the arc current was increased from 400 to 600 A. The feedstock (powder) and the coatings were predominantly composed of CaZrO₃ along with a minor amount of CaZr₄O₉ phase. The rise in the arc current resulted in a slight increase in the relative proportion of the CaZrO₃ phase. Also, the coating produced at arc current of 600 A exhibited highest crystallinity. The detailed XRD analysis of (002) and (200) reflections of the ferroelectric CaZrO₃ revealed the preferred orientation of crystals in the coatings. The presence of this texture is explained on the basis of shifting the unstable Zr⁴⁺ ion in oxygen octahedral cage preferably in one direction. The increase in the arc current decreased the coefficient of friction and, as a result, relatively better wear resistance was observed for the coating produced using higher arc current. Moreover, the coating fabricated using arc current of 600 A reduced the volumetric weight loss by 13 times during the wear test as compared to the substrate. Plasma sprayed CaZrO₃ coating not only enhanced the wear resistance of the stainless steel but also showed the potential to furnish a bioactive surface.     

Structural,dielectric and ferroelectric properties of Ba1−x(Bi0.5Na0.5)xTiO3 ceramics

Lead free Ba_1?x(Bi_0.5Na_0.5)_xTiO₃ (x=0, 0.02, 0.04, 0.06, 0.08, 0.1) ferroelectric ceramics were synthesized by conventional solid state reaction technique. Sintering was done at 1200 °C for 2 h in air atmosphere. The final products have tetragonal symmetry with decreasing c/a ratio confirmed by X-ray diffraction analysis. The grain size varies between 300 nm to 1000 nm for x=0 to 0.1. With increase in Bi_0.5Na_0.5TiO₃ [BNT] content, the room temperature permittivity decreases whereas the Curie temperature (T_c) increases and its highest value was found to be 155 °C for 10 mol% of BNT addition. The ceramics show stable and low dielectric loss characteristics. The remnant polarization (P_r) and the coercive field (E_c) increases monotonously with increase in BNT content. The highest value of 2P_r (=17 μC/cm²) and 2E_c (=22 Kv/cm) was obtained for x=10 mol% BNT addition.     

A continuous-time least mean-phase adaptive filter for power system frequency estimation

The mean squared error criterion is widely used in the literature. However, there are applications where the squared error is not the primary parameter affecting the performance of a system. In this paper, we introduce a cost function that is based on the phase error. The criterion is useful for applications where the performance depends primarily on the phase of the estimated (recovered) signal. A continuous-time adaptive filter is then developed using the proposed criterion in stochastic differential equation formalism. The proposed adaptive filter is used to estimate power system frequency where the formulated structure is very simple. The three-phase voltages are converted to a complex form for processing by the proposed algorithm. The performance of the new algorithm is studied through simulations at different situations of the power system.     

Seasonal and clonal variations in some major glycosidic bound volatiles in Kangra tea (Camellia sinensis (L.) O. Kuntze)

Seasonal and clonal variations in glycosidic bound volatile compounds were studied in tea clones representing the three different varieties viz. sinensis, assamica and cambodiensis grown in Kangra region. Glycosidic bound volatile compounds were characterised by GC–MS and quantification of major volatiles was done by GC. (E)-2-hexenal, benzyl alcohol, phenylethanol, linalool, linalool oxides, geraniol and methyl salicylate were the major glycosidic bound volatiles identified in tea shoot. Clonal variations in the quantity were observed in these bound volatiles. Seasonal variations were also observed in the quantity of bound volatiles in regional Kangra clone during three different growth flushes of tea. These variations in glycosidic precursors of volatile compounds were studied in context with orthodox made tea and its quality. These seasonal and clonal variations in precursors of volatile compounds can be directly correlated to the difference in the quality of tea made from these cultivars.     

Surface patch binding‐induced exfoliation of nanoclays and enhancement of physical properties of gelatin organogels

Nanoclay‐containing organogels were prepared by exfoliating layered silicate nanoclay (Laponite^® and montmorillonite, aspect ratio 30 and 250) in organogels made in glycerol solutions. Zeta potential of the binding profile between clay and gelatin chains in the milieu of glycerol was consistent with a surface patch binding mechanism. To achieve customized thermal and viscoelastic properties, optimum binding of nanoclay to gelatin was probed, and it was noticed that [clay] = 0.03% (w/v) and [glycerol] = 30% (v/v) produced the best results. Gelation temperature T_gel (Laponite organogels) increased from 28 to 34 °C (ca 21% change) with a concomitant increase in gel elastic modulus from 400 to 1200 Pa (ca 300% change). For montmorillonite organogels, it was possible to raise T_gel further to 43 °C (56% change). X‐ray diffraction data and Cole–Cole plots indicated that clay platelets were homogeneously exfoliated in the organogel matrix. Thus, the thermoviscoelastic properties of gelatin organogels could be modulated to raise the gelation temperature to 43 °C, and gel strength to 1200 Pa by the addition of nanoclay whose concentration may not exceed 0.03% (w/v). Considering the wide application of gelatin gels in pharmaceuticals, food preservation and personal care products, the aforesaid enhancement in physical properties is significant. © 2016 Society of Chemical Industry