Li2MnO3 content effects on thermal,structural, electrical and electrochemical properties of xLi2MnO3-(1-x)LiNi0.9Zn0.1O2 cathode materials

xLi₂MnO₃-(1-x)LiNi_0.9Zn_0.1O₂ (x = 0.1, 0.2 and 0.3) cathodes were prepared by two steps solid-state reaction method. Layered crystalline phases (space groups of C2/m for Li₂MnO₃ and R3m for LiNi_0.9Zn_0.1O₂) were detected in all cathodes. FTIR study also revealed the formation of the layered-type structures of all cathodes. The structural parameters were greatly influenced by the contents of Li₂MnO₃ in xLi₂MnO₃-(1-x)LiNi_0.9Zn_0.1O₂. The electrical conductivities were found in the range of 1.2 × 10^?6 to 2.7 × 10^?6 S/cm. The dielectric spectra revealed the interfacial polarization Maxwell–Wagner type dielectric dispersion existing in all samples. The cathodes delivered the discharge capacities of 149 (x = 0.1), 151 (x = 0.2) and 157 mAh/g (x = 0.3) with capacity retention between 94.6 and 96.8% when they were cycled from 3.0 to 4.5 V under 0.1C rate. The x = 0.3 cathode exhibited the highest cyclic performance (96.8%) after 10 cycles due to its lower cations disorder.     

Modification and validation of the mixed-format Engineering Concept Assessment for middle school students using many-facet Rasch measurement

Integrating engineering into the K-12 science curriculum continues to be a focus in national reform efforts in science education. Although there is an increasing interest in research in and practice of integrating engineering in K-12 science education, to date only a few studies have focused on the development of an assessment tool to measure students’ understanding of engineering design. Most of the existing measures focus only on knowledge and understanding of engineering design concepts using multiple-choice items with the exception of the mixed-format Engineering Concept Assessment (ECA). Also, advanced measurement models are lacking application in the testing of such mixed-format assessments in science education. This study applied many-faceted Rasch measurement to the modified ECA for eighth-grade (ECA/M8) and a newly constructed rubric applied by five judges across 497 eighth-grade students’ responses after experiencing an integrated learning unit on the engineering design process. The results supported the fit of the items and rubric rating scales to the Rasch specifications. Recommendations are made for item wording, and further reliability and validity testing of the ECA/M8, and use of the ECA/M8 in science education and research.     

Fractional-order excitable neural system with bidirectional coupling

Fractional-order dynamics is applicable to biological excitable systems with strong interactions or systems with long-term memory effect. The activity of neural membrane voltage depends on the long-range correlations of ionic conductances. Such a behavior of the membrane voltage with long-range correlation can be better described with a fractional-order dynamics. A fractional-order coupled modified three-dimensional (3D) Morris–Lecar (M–L) neural system has been presented to show the variations in the firing patterns from resting state \( \rightarrow \) oscillatory pattern \( \rightarrow \) bursting and the synchronous behavior by designing a bidirectional coupling mechanism. The fractional exponents are lying between 0 and 1. The predominant controller of the changes of firing behavior is the fractional exponent. The stability of synchronization and nature of the fractional system dynamics have been analyzed. To make the investigations more convincing and biologically plausible, we consider a network of M–L oscillators with bidirectional synaptic coupling functions using global type connections and present the effectiveness of the coupling scheme.     

Microwave digestion of “residual fuel oil” (NIST SRM 1634b) for the determination of trace elements by inductively coupled plasma-mass spectrometry

A microwave procedure for the digestion of the NIST 1634b reference material “residual fuel oil” in closed pressurized vessels was developed in an attempt to facilitate routine analysis and obtain reproducible conditions or comparable results. The influence of sample size, reagent composition and volume, microwave power, and duration of heating on the digestion procedure was studied. Pressure and temperature inside the reaction vessels were monitored to determine the progression of the reaction and to develop optimal conditions. A nine-step heating program requiring 36.5 min with microwave power not exceeding 450 W in the pulsed mode was found suitable for the digestion of ～ 250 mg fuel oil with a mixture of nitric acid (5.0 mL) and hydrogen peroxide (2.0 mL). The reproducibility of microwave power was determined in terms of the relative standard deviations (n = 3) for temperature (2.7%) and pressure (4.9%) data. The vapor pressures obtained with 5.0 mL Milli-Q water (heated) in an 80-mL digestion vessel showed good agreement with literature data. The excess acid in the resulting digests was removed by evaporation and the concentrations of 24 elements (Ag, Al, As, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mo, Ni, Pb, Sb, Sn, Sr, Ti, Tl, V, U, and Zn) were determined in the diluted digests by inductively coupled plasma mass spectrometry (ICP-MS). The experimental results were in good agreement with the certified and recommended concentrations for eight elements (Al, As, Co, Cr, Ni, Pb, V, Zn) in solutions obtained after one digestion step. An additional digestion step, consisting of intermediate cooling and venting stages, was required for the accurate determination of Fe. No agreement was reached for Ca and Ba even after two-step digestion. The proposed method of digestion provided precise results with relative standard deviations generally less than 5% for most of the elements determined.     

Microwave digestion of "residual fuel oil" (NIST SRM 1634b) for the determination of trace elements by inductively coupled plasma-mass spectrometry

A microwave procedure for the digestion of the NIST 1634b reference material "residual fuel oil" in closed pressurized vessels was developed in an attempt to facilitate routine analysis and obtain reproducible conditions or comparable results. The influence of sample size, reagent composition and volume, microwave power, and duration of heating on the digestion procedure was studied. Pressure and temperature inside the reaction vessels were monitored to determine the progression of the reaction and to develop optimal conditions. A nine-step heating program requiring 36.5 min with microwave power not exceeding 450 W in the pulsed mode was found suitable for the digestion of approximately 250 mg fuel oil with a mixture of nitric acid (5.0 mL) and hydrogen peroxide (2.0 mL). The reproducibility of microwave power was determined in terms of the relative standard deviations (n = 3) for temperature (2.7%) and pressure (4.9%) data. The vapor pressures obtained with 5.0 mL Milli-Q water (heated) in an 80-mL digestion vessel showed good agreement with literature data. The excess acid in the resulting digests was removed by evaporation and the concentrations of 24 elements (Ag, Al, As, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mo, Ni, Pb, Sb, Sn, Sr, Ti, Tl, V, U, and Zn) were determined in the diluted digests by inductively coupled plasma mass spectrometry (ICP-MS). The experimental results were in good agreement with the certified and recommended concentrations for eight elements (Al, As, Co, Cr, Ni, Pb, V, Zn) in solutions obtained after one digestion step. An additional digestion step, consisting of intermediate cooling and venting stages, was required for the accurate determination of Fe. No agreement was reached for Ca and Ba even after two-step digestion. The proposed method of digestion provided precise results with relative standard deviations generally less than 5% for most of the elements determined.     

1,3‐Ninhydrin dihydrazone featuring an R44(12) motif with symmetry and comprising only N and H atoms

In the title compound [systematic name: (1Z,3Z)‐1,3‐dihydrazinylidene‐1H‐inden‐2(3H)‐one], C₉H₈N₄O, isolated molecules possess approximate noncrystallographic C_2v symmetry and their cis conformation and planarity are assisted by a pair of short intramolecular N—H...O hydrogen bonds. Each molecule is asymmetrically involved in an extensive three‐dimensional network of N—H...O and N—H...N hydrogen bonds, and the structure also exhibits weaker π–π and C=O...C interactions. The structure features an R₄⁴(12) motif consisting solely of N and H atoms and possessing crystallographic symmetry.