Defect-induced asymmetry of local hysteresis loops on BiFeO<Subscript>3</Subscript> surfaces

Local piezoresponse hysteresis loops were systematically studied on the surface of ferroelectric thin films of BiFeO₃ grown on SrRuO₃ and La_0.7Sr_0.3MnO₃ electrodes and compared between ultrahigh vacuum and ambient environment. The loops on all the samples exhibited characteristic asymmetry manifested in the difference of the piezoresponse slope following local domain nucleation. Spatially resolved mapping has revealed that the asymmetry is strongly correlated with the random-field disorder inherent in the films and is not affected by the random-bond disorder component. The asymmetry thus originates from electrostatic disorder within the film, which allows using it as a unique signature of single defects or defect clusters. The electrostatic effects due to the measurement environment also contribute to the total asymmetry of the piezoresponse loop, albeit with a much smaller magnitude compared to local defects.     

GRINDING OF NICKEL-BASED SUPER-ALLOYS AND ADVANCED CERAMICS

This paper studies grinding of Inconel 718, Hastelloy, and some advanced ceramics. A newly developed ultra-high-speed grinding machine and a conventional grinding machine were used for the experiments. The ultra-high-speed grinding machine is equipped with a specially designed and built spindle unit that can run up to 200 m sec^-1 and deliver a maximum output of 12 kW. The surface roughness and residual stress values of the ground super-alloys and advanced ceramics were measured using a profilometer and a residual stress analyzer, respectively. The ground surfaces were also assessed using a scanning electron microscope. The effect of h_m (undeformed chip thickness) on surface topography of the difficult-to-machine materials was also investigated. A higher grinding wheel speed produces a smaller cutting depth and undeformed chip thickness, and thus smaller grinding force, decreased residual surface stress, and better surface finish. High productivity and good surfaces with ductile streaks could be obtained by employing ultra-high-speed grinding, even at very large wheel depths of cut such as 400 μm, without cross feed.     

Applicability of Various Approximate Methods to the Solution of the Waveguide Equation

Abstract

Several possible methods for the solution of the planar waveguide equation in non-trivial cases are examined and a distinction is made between ‘exact’ (converging) solutions and other approximate methods whose accuracies depend on the shape of refractive-index profile involved. Among the exact solutions the equivalence of the dark- and bright-mode methods is examined, thereby identifying the dark reflectivity spikes, predicted by the reflectivity method, with the modes of propagation. A heuristic treatment of the phase integral in the WKB approximation is given and definite conclusions are reached as to its applicability in the solution of the waveguide equation for various profile shapes. An alternative method, involving perturbation theory, is suggested for use with steep sided profiles like the ones created by ion-exchange or epitaxial growth for which the WKB approximation is shown to be totally unsuitable.     

Visco‐Elastic and Flow Properties of Gelatin from the Bone of Freshwater Fish (Cirrhinus mrigala)

The average yield of gelatin from the bone of freshwater fish (Cirrhinus mrigala) was 6.13%. The fluorescence spectra revealed maximum emission at 303 nm indicating the exposure of chromophores to bulk solvent. The amino acid profile of gelatin revealed a higher proportion of glycine and imino acids. The bloom strength of gelled gelatin was 159.8 g. The average molecular weight of fish bone gelatin was 281 kDa as determined by gel filtration technique. The dynamic oscillatory test of gelatin solution as a function of time and temperature revealed gelling and melting temperatures of 8.0 °C and 17.0 °C, respectively. The flow behavior of gelatin solution as a function of concentrations and temperatures revealed non‐Newtonian behavior with pseudo‐plastic phenomenon. The Herschel–Bulkley and Casson models were found suitable to study the flow behavior. The emulsion capacity (EC) of gelatin was inversely proportional to its concentration.     

Direct Observation of the Dynamic Compressive Failure of a Transparent Polycrystalline Ceramic (AlON)

High-speed photography has been used to observe the dynamic failure of uncoated and Cr-coated transparent polycrystalline aluminum oxynitride (AlON) material, undergoing uniaxial, high-strain rate compression with a modified compression Kolsky bar technique. The high-speed photographs are correlated in time with measurements of the stresses in the specimen. In the fully transparent samples, the dynamic activation, growth, and coalescence of cracks and resulting damage zones from spatially separated internal defects have been directly observed and correlated to the macroscopic loss of the load-carrying capacity and ultimate catastrophic failure of this material. Identical experiments on the coated material only show the dynamic progressive failure on the specimen surface and do not show the origin of the failure images at the internal defects.     

Gharats (watermills): Indigenous device for sustainable development of renewable hydro-energy in Uttrakhand Himalayas

The Himalaya has a rich ancient tradition for tapping hydro-energy from the hill streams and rivers through the device of gharats (watermills). The present contribution encompasses the study on the energy consumption pattern of hill communities living in buffer zone of the Nanda Devi Biosphere Reserve, a world heritage site located in Garhwal Himalayas, India, The current status of gharats, the factors responsible for the neglect of this renewable energy device, initiatives taken for upgrading for their revival have been highlighted. Field and policy level opportunities and constraints associated with promotion of such hydro-energy in the study area by upgrading of traditional watermills are analysed and suitable options for removing impediments are suggested.     

Antioxidant and antimicrobial activity of pomegranate peel extract improves the shelf life of chicken products

The antioxidant and antimicrobial potential of pomegranate peel and seed extract was investigated. Pomegranate peel extract (PE) showed excellent antioxidant activity while the seed extract (PS) did not have any significant activity. The IC₅₀ value of PE for 2,2‐diphenyl‐1‐picrylhydrazyl radical scavenging was 4.9 μg mL^–1 while that of Butylated hydroxy toluene was 21.2 μg mL^–1, indicating that it was a stronger antioxidant. The efficacy of PE in scavenging hydroxyl and superoxide anion radical was also very high. It also had good reducing power and iron chelation capacity. PE showed good antimicrobial activity against Staphylococcus aureus and Bacillus cereus having minimum inhibitory concentration of 0.01%. Pseudomonas could be inhibited at a higher concentration of 0.1% while it was ineffective against Escherichia coli and S. typhimurium. Addition of PE to popular chicken meat products enhanced its shelf life by 2–3 weeks during chilled storage. PE was also effective in controlling oxidative rancidity in these chicken products.     

Room temperature ferromagnetic behavior,linear and nonlinear optical properties of KNbO3 microrods

Microrods of potassium niobate (KNbO₃) were synthesized at 700, 800 and 900 °C by solid state reaction method and their structural, morphological, linear optical, nonlinear optical and magnetic properties were studied. X-ray diffraction and Rietveld refinement reveal that all the prepared KNbO₃ samples belong to single phase orthorhombic structure with space group of Cm2m. Fourier transform infrared and Raman spectral analyses confirmed the Nb-O symmetric stretching vibrational modes of NbO₆ octahedron. The grain growth direction (001) and inter planar spacing (0.38 nm) of KNbO₃ were determined by high resolution transmission electron microscopy. Field emission scanning electron microscopy images revealed that KNbO₃ are formed with nearly rod shape morphology with average diameter varying from 471 to 678 nm and length lies between 1.2 and 2.3 µm. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy studies confirmed the presence of K, Nb and O elements in the KNbO₃ matrix. UV–visible diffuse reflectance spectra showed that the band gap of KNbO₃ microrods varies between 3.18 and 3.22 eV. The existence of blue (492 nm) and green (521 nm) emissions evidently showed the presence of oxygen vacancy in the samples. All the synthesized KNbO₃ microrods exhibited relatively high SHG efficiency as compared with that of the standard KDP. Vibrating sample magnetometer analysis showed the existence of ferromagnetic behavior at room temperature. The saturation magnetization (M_s) of KNbO₃ microrods lies between 0.015 and 0.012 emu g^?1 and coercive field (H_c) varies in the range from 489 to 420 Oe.