Carbon xerogels as electrodes for supercapacitors. The influence of the catalyst concentration on the microstructure and on the electrochemical properties

Carbon xerogels, synthesized through the resorcinol–formaldehyde polycondensation and subsequently dried under subcritical condition, have been studied as electrodes for supercapacitors. In particular, the influence of the catalyst concentration has been investigated by systematically changing the amount of catalyst (Na₂CO₃) utilized to synthesize the xerogels. To clarify the effect of such variable, both the surface properties and the electrochemical behavior of xerogel-based supercapacitors have been examined. From the xerogels characterization, it can be inferred that the amount of catalyst used has a strong influence on the properties of the material. Contrary to what happens with carbon aerogels, the best properties are obtained with the xerogels synthesized with the least amount of catalyst: in this case the highest measured specific capacitance of the supercapacitor cells, which is assembled coupling two symmetric electrodes in series, is 25 F/g, value that corresponds to a single-electrode specific capacitance of 100 F/g. The maximum energy storage capacity in an aqueous electrolyte is 3.1 Wh/kg. Using more concentrated catalyst solutions, the gel microstructure becomes finer, composed of smaller particles and pores, which in turns leads to an increase of the capillary drying stresses and to the collapse of the organic structure. Consequently, the shrinkage of the gels is high and the final carbon xerogels do not posses sufficient surface area and porosity to store a significative amount of energy.     

Study of the thermal initiation of ammonium dinitramide (ADN) crystals and prills

Abstract

The thermal initiation by electron beam heating (and calibrated hot stage), of single crystals and prills of ADN, has been filmed / recorded in an Environmental Scanning Electron Microscope, from the formation of microscopic “reaction sites” (0.01 μm in diameter) to full crystal consumption. The transformations of the ADN prills and crystals were compared and recorded in real time at various magnifications (x10,000-100) and under different atmospheres (pure nitrogen and nitrogen/water vapour mixtures). The initiation characteristics of the prills and crystals were found to differ and are related to the microstructural characteristics produced by different prill manufacturing techniques namely, the “prilling tower” technique (Thiokol) and the “melt-stir” technique (CSD).     

Survival and reproduction of lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) on flora associated with native habitats in Kansas

Capture of Rhyzopertha dominica in pheromone-baited traps located many kilometers away from grain storage suggests that this species may be exploiting non-grain food sources. To investigate the potential for survival of this species on alternative hosts in the absence of grain, we conducted no-choice feeding assays with twigs and seeds of trees, and seeds of grasses, forbs, and shrubs, commonly encountered on Kansas prairie landscapes where R. dominica has been captured. In addition, R. dominica development and progeny production were assessed on seeds that adults were able to survive on for at least two weeks. Adult survival was poor on grass and forb seeds, although 13.4% of individuals survived on Elymus canadensis, Canada wildrye, seeds after two weeks, compared with 80.3% on Triticum aestivum, wheat, and 0.0% survival in the absence of food. Beetles readily tunneled into twigs from a wide range of tree species, but survival was generally low. A few individuals survived up to four weeks on Gleditsia triacanthos, honey locust. In contrast, bioassays showed that R. dominica could survive and reproduce on damaged seeds (acorns) of six species of oak, but not on undamaged seeds. For example, survival was 95.8% on damaged Quercus muehlenbergii, chinquapin oak. A survey of acorns at the original field collection site showed that the majority of the acorns on the ground had been cracked or bored into by insects and small mammals. Furthermore, we recovered three R. dominica adults from acorns collected in the field and held in sealed containers in the laboratory. These findings suggest that R. dominica populations in Kansas can persist on wild acorns when grain is not available.     

FPGA implementation of current-sharing strategy for parallel-connected SEPICs

The attempt echoes to evolve an equal current-sharing algorithm over a number of single-ended primary inductance converters connected in parallel. The methodology involves the development of state-space model to predict the condition for the existence of a stable equilibrium portrait. It acquires the role of a variable structure controller to guide the trajectory, with a view to circumvent the circuit non-linearities and arrive at a stable performance through a preferred operating range. The design elicits an acceptable servo and regulatory characteristics, the desired time response and ensures regulation of the load voltage. The simulation results validated through a field programmable gate array-based prototype serves to illustrate its suitability for present-day applications.     

Nonsupercritically Dried Silica–Alumina Aerogels—Effect of Gelation pH

Silica–alumina mixed oxide aerogels, with 5, 10, 15, 20, and 25 wt% of alumina in silica, have been synthesized by a hybrid sol–gel technique followed by subcritical drying. The gelation has been carried out under pH values of 3 and 5. pH is a decisive parameter that affects the rate of hydrolysis and condensation of alkoxides. Moreover, it also influences the surface area and porosity features of the final material. The gelation time has been found to be much longer for gels that were gelled at pH 3. Nitrogen sorption studies of the aerogels calcined at 500°C indicate that the mixed oxide aerogels are mesoporous in nature and the gels prepared under a gelation pH of 3 have been found to have higher surface area than the pH 5 counterpart. Transmission electron microscopy and X-ray diffraction analysis have been performed to verify the homogeneity of the mixed oxide aerogel.     

Rheological properties of black gram (Phaseolus mungo) batter: characterisation of flour from native and modified rice and their effect on batter viscosity

Rheological properties of black gram batter as a function of soaking time, and effect of flour from native and thermally modified rice on black gram batter have been studied. Greater increase in hydration capacity of black gram dhal was observed during 5–15 min of soaking, a gradual increase up to 90 min and a marginal increase beyond this period. Apparent viscosity of batter showed 100% increase up to 90 min and less than 20% increase beyond 120 min, and shear‐thinning nature of batter indicated that they were pseudo‐plastic in nature. Yield stress and consistency index showed greater changes after 90 min, while flow behaviour index did not show significant change beyond 90 min of soaking. Compared with the addition of native rice flour, incorporation of flaked rice flour and expanded rice flour into black gram batter significantly increased the cold paste viscosity of the batter, probably because of their greater water‐holding capacity, compared with that from native rice. Differences in physicochemical characteristics and pasting behaviour of these flour slurries, as studied by Rapid Visco Analyser, corroborated these results by the typical profile of pregelatinised products for flaked rice and expanded rice in comparison to native rice.     

Data Analysis and Interpretation in IoT-Based Systems for Critical Medical Services and Healthcare Applications

Wireless Personal Communications - The use of Internet of things in health care is a major breakthrough as it can help us save a lot of lives that can be prevented because of prolonged commute...     

Effect of high‐pressure treatment on trypsin hydrolysis and antioxidant activity of egg white proteins

High‐pressure processing (HPP) is known to modify the functional properties of the proteins by changing its structure that can lead to protein denaturation, aggregation or gelation, depending on the protein system and the applied pressure. The potential to modify functional properties of protein and their products using HPP has been explored widely in last decade. In this study, the effect of HPP on the degree of trypsin hydrolysis (DTH) and antioxidant activity (AA) of egg white protein (EWP) and freeze‐dried egg white powder (DEW) was evaluated. EWP and DEW were subjected to trypsin hydrolysis for up to 120 min, with and without HP treatments [pressure level (350–550 MPa) and treatment time (5–15 min)]. HP treatment caused substantial increase in DTH of EWP and DEW, increasing it from 2.78% (EWP control) and 2.20% (DEW control) to 11.3% (HP‐treated EWP) and 8.41% (HP‐treated DEW), respectively. HP treatment also had an emphatic effect on AA of EWP (concentration 10% w/v) with AA increasing from 9.34% for control EWP to 19.0% after 5‐min HP treatment at 350 MPa and 25.00% after the same treatment at 550 MPa. Overall, HPP caused an increase in DTH and AA of EWP and DEW over the control. SDS‐PAGE and differential scanning calorimetric studies confirmed the effect of HP on the hydrolysis of egg proteins.