Dielectric and impedance spectroscopy of barium orthovanadate ceramics

Barium orthovanadate (Ba₃V₂O₈), a derivative of perovskite family has been prepared using a mixed-oxide technique. The room temperature X-ray diffraction analysis has confirmed the formation of a single phase compound in trigonal crystal structure. The study of microstructure by scanning electron microscopy shows that the compound has well defined grains, distributed uniformly throughout the surface. The studies of dielectric parameters (ε_r and tan δ) of the compound as a function of temperature at three different frequencies (100, 500, 1,000 kHz) exhibit that they are almost temperature independent at low and medium temperature ranges. Detailed studies of impedance and related parameters exhibit that the electrical properties of the material are strongly dependent on temperature, and bear a good correlation with its microstructures. The bulk resistance, evaluated from complex impedance spectra, is found to be decreasing with rise in temperature. It shows that the material has negative temperature co-efficient of resistance similar to that of semiconductors. The same behaviour has also been observed in the study of I–V characteristics of the material. The complex electric modulus analysis indicates the possibility of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius behavior of the material. The ac conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law.     

Friction stir scribe welding technique for dissimilar joining of aluminium and galvanised steel

Friction stir scribe technology, a derivative of friction stir welding, was applied for the dissimilar lap welding of an aluminium alloy and galvanised mild steel sheets. During the process, the rotating tool with a cobalt steel scribe first penetrated the top material – aluminium – and then the scribe cuts the bottom material – steel. The steel was displaced into the upper material to produce a characteristic hook feature. Lap welds were shear tested, and their fracture paths were studied. Welding parameters affected the welding features, including hook height, which turned out to be highly related to fracture position. Therefore, in this paper, the relationships among welding parameters, hook height, joint strength and fracture position are presented. In addition, the influence of zinc coating on joint strength was also studied.     

Experimental and thermal analysis of energy efficient novel design wet cooling towers

Waste heat is generally dissipated from process water to atmospheric air in cooling towers. In the present study, a novel design is used to extract more amount of heat without any additional energy input by incorporating secondary ambient air in an induced draft wet cooling tower. In addition, more fresh air is induced in the tower from the rain zone, which increases the effectiveness at any value of the water to air flow rate (L/G ratio). Moreover, tower characteristics, range, and evaporation loss were also increased due to the novel design. It is noteworthy that secondary fresh air increases effectiveness, heat rejection, and tower characteristics by 10.12%, 19.65%, and 26.11%, respectively, and decreases approach by 16.32% at 0.55 L/G ratio, 44°C inlet water temperature, 29.7°C dry bulb temperature, and 18.4°C inlet air wet bulb temperature.     

Reproducible,biocompatible medical materials from biologically derived polysaccharides: Processing and Characterization

Natural polysaccharides like chitosan and dextran have garnered considerable interest in biomedical applications due to their biocompatibility, biodegradability, and nontoxicity. Nonetheless, the development of a reproducible class of medical devices from these materials is challenging and has had limited success. Chitosan and dextran are inherently variable and synthesis using these materials is prone to inconsistencies. In this study, we put forward a robust product development regimen that allows these natural materials to be developed into a reproducible class of biomaterials. First, an array of validated characterization methods (Proton Nuclear Magnetic Resonance, titrations, Ultraviolet spectroscopy, Size Exclusion Chromatography—Multi-Angle Light Scattering, Size Exclusion Chromatography—Refractive Index, and proprietary methods) were developed that allowed rigorous specifications to be set for unprocessed chitosan and dextran, chitosan and dextran intermediates, and chemically modified materials—acrylated chitosan (aCHN) and oxidized dextran (oDEX). Second, a robust and reproducible synthesis scheme involving various in-process controls was developed to chemically modify the unprocessed polysaccharides. Third, purification methods to remove byproducts and low-molecular-weight impurities for both aCHN and oDEX were developed. The study presents a viable strategy for converting variable, natural materials into a reproducible class of biomaterials that can be applied in various biomedical applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48454.     

A new interpretation of interferometric fringe patterns

The interferometric method of Nisida and Saito, the absolute retardation method of Post and the double-exposure holo-interferometric method of Hovanesian, Brcic and Powell are correlated and shown to give identical fringe patterns as regards intensity. Various discrepancies in Nisida and Saito's interpretation of their fringe patterns are pointed out, and the simultaneous presence and relative predominance of isochromatic and isopachic half-tones are discussed. The principles of photography and the concept of half-tones are used to explain the formation of concomitant isochromatics and isopachics and to give a new interpretation to these fringe patterns.     

Graft copolymerization onto starch. II. Grafting of acrylonitrile to granular native potato starch by manganic pyrophosphate initiation. Effect of reaction conditions on grafting parameters

The effect of reaction conditions on the composition of native potato starch–polyacrylonitrile graft copolymers initiated by manganic pyrophosphate onto starch slurries at 30°C has been examined. In general, when the Mn³⁺ ion concentration was increased from 0.15 × 10^?3M to 3.0 × 10^?3M (other conditions kept constant), an increase in conversion of monomer to polymer and % add-on was observed, whereas frequency of grafts (anhydroglucose units, AGU, per grafted chain) decreased. Also, the average molecular weights of grafts showed a decrease from 2.2 × 10⁵ to 1.5 × 10⁵. Increasing the concentration ratio of starch to monomer during polymerization by a factor of 3 produced an increase in the conversion of monomer to polymer, whereas an increase in frequency of grafts (AGU/chain) was obtained. Values of % add-on and average molecular weights of the grafts showed, however, a decreasing tendency. It was observed that grafting onto starch took place readily even at acid additions as low as 10 × 10^?3M H₂SO₄ (pH ?1.8). Selective solvent extraction of homopolymer and extremely low conversions of monomer to polymer (0.1%–1.5%) in duplicate runs without addition of starch indicated that grafting efficiencies were high in all cases. An attempt has been made to interpret the results in terms of variations in factors such as initial ratio of (Mn³⁺)/(AGU), termination rate of acrylonitrile chain radicals by oxidation by Mn³⁺ ions, oxidation rate of radicals formed on anhydroglucose units by Mn³⁺ ions, and physical factors such as diffusion rate of Mn³⁺ ions through the polyacrylonitrile-grafted starch granules for terminating the radicals.     

Development of electronic materials from industrial waste red mud

The current research work presents the preparation and characterization of some new electronic materials using bismuth oxide (Bi₂O₃) and industrial waste red mud in different proportion by weight using a cost-effective mixed-oxide technique. Preliminary X-ray structural analysis exhibits the formation of compounds with structure analogous to that of BiFeO₃ compound along with some impurity phases. Studies of dielectric parameters (ε_r and tanδ) of these compounds as a function of temperature and frequency exhibit that they are almost temperature independent in the low temperature range and possess high relative permittivity with low loss in the high temperature range. Detailed studies of impedance and related parameters exhibit that the electrical properties of these materials are strongly dependent on temperature, and bear a good correlation with their microstructures. The bulk resistance, evaluated from complex impedance spectra, is found to be decreasing with rise in temperature, exhibiting a typical negative temperature co-efficient of resistance (NTCR)—type behavior similar to that of semiconductors. Studies of electric modulus indicate the presence of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The low leakage current and NTCR behavior of the sample have been verified from I–V characteristics. The nature of variation of dc conductivity with temperature confirms the Arrhenius and NTCR behavior in the material. The ac conductivity spectra show a typical-signature of an ionic conducting system, and are found to obey Jonscher’s universal power law.     

Second generation waste package design and storage concept for the Yucca Mountain Repository

The reference waste package design and operating mode to be used in the Yucca Mountain Repository is reviewed. An alternate (second generation) operating concept and waste package design is proposed to reduce the risk of localized corrosion of waste packages and to reduce repository costs. The second generation waste package design and storage concept is proposed for implementation after the initial licensing and operation of the reference repository design. Implementation of the second generation concept at Yucca Mountain would follow regulatory processes analogous to those used successfully to extend the design life and uprate the power of commercial light water nuclear reactors in the United States. The second generation concept utilizes the benefits of hot dry storage to minimize the potential for localized corrosion of the waste package by liquid electrolytes. The second generation concept permits major reductions in repository costs by increasing the number of fuel assemblies stored in each waste package, by eliminating the need for titanium drip shields and by fabricating the outer container from corrosion resistant low alloy carbon steel.     

Use of the false discovery rate for evaluating clinical safety data

Clinical adverse experience (AE) data are routinely evaluated using between group P values for every AE encountered within each of several body systems. If the P values are reported and interpreted without multiplicity considerations, there is a potential for an excess of false positive findings. Procedures based on confidence interval estimates of treatment effects have the same potential for false positive findings as P value methods. Excess false positive findings can needlessly complicate the safety profile of a safe drug or vaccine. Accordingly, we propose a novel method for addressing multiplicity in the evaluation of adverse experience data arising in clinical trial settings. The method involves a two-step application of adjusted P values based on the Benjamini and Hochberg false discovery rate (FDR). Data from three moderate to large vaccine trials are used to illustrate our proposed 'Double FDR' approach, and to reinforce the potential impact of failing to account for multiplicity. This work was in collaboration with the late Professor John W. Tukey who coined the term 'Double FDR'.