Dielectric relaxation and conduction mechanism of complex perovskite Ca0.90Sr0.10Cu3Ti3.95Zn0.05O12 ceramic

In this work, Sr and Zn co-doped calcium copper titanate having nominal formula Ca_0.90Sr_0.10Cu₃Ti_3.95Zn_0.05O₁₂ has been synthesized and systematically studied for structure, dielectric and electrical properties. The phase purity of the prepared composition has been confirmed by X-ray diffraction (XRD) pattern and various structural parameters are presented here with Rietveld refinement data. The Scanning electron microscopy (SEM) image revealed the presence of homogeneous fine-grained microstructure investigated in the prepared ceramic. The impedance data well fitted with 2 R-CPE model confirmed the non-ideality of the system. Dielectric studies have shown the existence of two relaxation processes in low and high frequency domains. Low frequency dielectric response proposed as a combination of Maxwell-Wagner relaxation and intrinsic defect (V_o⁺⁺) while high frequency behavior has been interpreted in terms of polaronic relaxation caused by hopping process of an electron between Ti³⁺ and Ti⁴⁺ states. The frequency dependent behavior of conductivity has been well fitted to Dong’s model and interpreted in term of Overlapping Large Polaron Tunneling (OLPT) mechanism. The various parameters; relaxation angular frequency (ω₁) of Debye process, ionic hopping frequency (ω₂₎, dc conductivity (σ_o), cole- cole parameter (α) and frequency exponent (s) have been determined by Dong’s Model fitting.     

Relationship between physicochemical and rheological properties of starches from Indian wheat lines

Starches from nine Indian wheat lines were evaluated to study the relationships between physicochemical and rheological properties. Large granules (>15 μm) were present in the highest proportion followed by medium (5–15 μm) and small granules (<5 μm). Amylose content ranged between 27.4 and 37.2%. Starch with the highest proportion of large granules (68.9%) showed higher values of G′_peak (576 Pa) and G′_final (432 Pa). Amylose content showed positive relationships with retrogradation, gel firmness, gumminess and adhesiveness while negative with springiness. Cooked starch pastes with the highest amylose content (37.2%) had higher ΔH_ret (0.88 J g^?1), G′_ret (361 Pa), adhesiveness (1.48 Ns), firmness (0.45 N) gumminess (0.22 N) and the lowest springiness (0.88). Amylose–lipid complex (AML) dissociation showed negative relations with swelling power, G′_peak, G′_breakdown and breakdown viscosity (r = ?0.779, ?0.66, ?0.771 & ?0.775, respectively, P < 0.05) while positive relationship with pasting temperature (r = 0.775, P < 0.05).     

Effect of interface coupling between polarization and magnetization in La0.7Pb0.3MnO3 (LPMO)/P(VDF-TrFE) flexible nanocomposite films

Journal of Materials Science - La0.7Pb0.3MnO3(LPMO) nanoparticles (NPs) were prepared by sol–gel auto-combustion method. These were embedded in P(VDF-TrFE) to form (0–3) nanocomposite...     

Structural investigation and giant dielectric response of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramic by Nd/Zr co-doping for energy storage applications

High performance dielectric materials are highly required for practical application for energy storage technologies. In this work, high-k pristine and modified calcium copper titanate having nominal formula Ca_0.95Nd_0.05Cu₃Ti_4?xZr_xO₁₂ (x?=?0.01, 0.03 & 0.10) were synthesized and characterized for structural and dielectric properties. Single phase formation of the synthesized compositions was confirmed by X-ray diffraction patterns and further analysed using Rietveld refinement technique. Phase purity of the synthesized ceramics was further confirmed by Energy-dispersive X-ray Spectroscopy (EDX) analysis. SEM images demonstrated that grain size of the modified CCTO ceramics was controlled by Zr⁴⁺ ions due to solute drag effect. Impedance spectroscopy was employed to understand the grain, grain boundaries and electrode contribution to the dielectric response. Nyquist plots were fitted with a 2R-CPE model which confirms the non-ideality of the system. Substitution of specific concentration of Nd and Zr improved the dielectric properties of high dielectric permittivity (ε′ ~?16,902) and minimal tanδ (≤?0.10) over a wide frequency range. The giant ε′ of the investigated system was attributed to internal barrier layer capacitance (IBLC) effect and reduced tanδ accredited to enhanced grain boundaries resistance due to substitution of Zr⁴⁺ ions at Ti⁴⁺ site.     

Correlation between spin–phonon coupling and magneto-electric effects in CoFe2O4/PMN-PT nanocomposite: Raman spectroscopy and XMCD study

We have investigated strain-induced spin lattice coupling in the CoFe₂O₄/0.65Pb (Mg_1/3Nb_2/3)O₃–0.35PbTiO₃(PMN-PT) composite system, evident by temperature-dependent Raman spectroscopy and magnetization measurements. The strain interactions lead to magneto-electric coupling, and the measured magneto-electric voltage coefficient is 40 mV/cm^?1Oe^?1 for the CoFe₂O₄/PMN-PT composite samples. X-ray magnetic circular dichroism (XMCD) analysis establishes modified spin structure in the electrically poled CoFe₂O₄/PMN-PT composite, further validating the coupling between magnetic and electric ordering in the composite. The magneto-electric coupling coefficient α vs dc magnetic field curves revealed hysteretic behavior and enhanced α values after electric poling, which originates from the strain-induced modifications in the magnetic structure of composite in the electrically poled samples. These findings suggest that the existence of spin lattice coupling may lead to the mechanism of strong magneto-electric effects via strain interactions in CoFe₂O₄/PMN-PT composite.

     

Objective evaluation of the outcome of endopyelotomy using Whitaker's test and diuretic renography

OBJECTIVES: To assess the role of Whitaker's test (WT) and 99mTc-diethylene triamine penta-acetic acid diuretic renography (DRG) in determining objectively the outcome of endopyelotomy, and to rationalize the frequency and timing of such evaluation after endopyelotomy. PATIENTS AND METHODS: Thirty-one patients (age > 15 years) were prospectively evaluated after percutaneous endopyelotomy. WT was performed at 4-6 weeks via the nephrostomy maintained for external drainage, 24 h after removing the splint. DRG was performed at 3, 6 and 12 months, and then annually. RESULTS: WT performed 24 h after removing the splint diagnosed pelvic pressures in the unobstructed range (< 15 cmH2O) in 21 of the 24 patients were also evaluated with DRG at 3 months. An intra-pelvic pressure of > 15 cmH2O was correlated with a pattern of obstruction on DRG in all three units. Despite an unobstructed WT in 18 patients, categorization of DRG drainage showed disparity in six cases. All six renal units had a large pelvic area (> 15.0 cm2 in two and > 20.0 cm2 in four) and/or a poor renal function (separate glomerular filtration rate [GFR] of < or = 25 ml/min in four of the six units). The drainage pattern on DRG was unevaluable in two renal units as the function was poor (separate GFR < 15 ml/min). During the first year, the drainage pattern on DRG improved in four cases. When followed beyond one year, the drainage pattern deteriorated at 2 years in only one of 14 evaluated renal units with an initial unobstructed WT. CONCLUSION: Using objective methods of evaluation, endopyelotomy was successful in relieving obstruction in 87% of cases. If inaccuracies in the interpretation of DRG, i.e. a large pelvic capacity and poor renal function, are accounted for, the results of WT as early as 24 h after removal of the splint correlated with DRG. Drainage patterns on DRG did not deteriorate during the first year. An early post-operative evaluation with WT or DRG, as appropriate, is thus sufficient evidence of the success of the procedure. Evaluations repeated during the first year after endopyelotomy may be unnecessary.     

A cost‐effective attack matrix based key management scheme with dominance key set for wireless sensor network security

To guarantee the proper functionality of wireless sensor network even in the presence of the potential threats, a well‐designed key management scheme is very important. The assumptions about attackers critically influence the performance of security mechanisms. This paper investigates the problem of node capture from adversarial view point in which the adversary intelligently exploits the different vulnerabilities of the network to establish a cost‐effective attack matrix. To counteract such attacks, the defender or the network designer constructs similar attack matrix. The defender will identify a set of critical nodes and use the key compromise relationship to assign a key dominance rank to each node of the network. The key dominance rank quantifies the possibility of attack on a particular node. It is used to determine the hash chain length. It is also used to improve the security of path key establishment as well as rekeying of the proposed scheme. The performance of the proposed scheme is analyzed with other existing schemes, and it is shown that it outperforms with increased resilience against node capture, reduced number of hash computations, reduced key compromise probability of proxy nodes, and reduced number of revoked links during rekeying process.     

Multiobjective Optimal Fuzzy Logic Controller Driven Active and Hybrid Control Systems for Seismically Excited Nonlinear Buildings

The third generation benchmark control problem for seismically excited nonlinear buildings is an effort to evaluate the developed control strategies in order to apply them in field applications. As the fuzzy logic control systems have been applied effectively in various fields, including vibration control of structures, a multiobjective optimal fuzzy logic control system has been proposed in this paper. Two types of control devices, namely, active and hybrid, driven by a fuzzy logic controller (FLC) have been considered in the present study. Nondimensionalized peak interstory drift ratio and peak floor acceleration have been used as the two objective functions for the multiobjective optimal design problem. A two-branch tournament genetic algorithm has been used to find a set of Pareto-optimal solutions, as the optimization problem is not necessarily continuous or convex. Performance of the FLC driven active and hybrid control systems have been evaluated for all three third generation benchmark problems for seismically excited nonlinear buildings (3-, 9- and 20-story). Acceleration and velocity information of different floors have been used as feedback to the FLC. This approach provides a set of Pareto optimal designs, from which a controller design can be selected for the required performance. The FLC driven active control system performs better than the sample controller given in the benchmark problem. Though the number of sensors and control devices are far less, the performance of the hybrid is close to the active control system.