Homogeneous anisotropic cosmological models with variable gravitational and cosmological “Constants”

The Einstein field equations with perfect fluid source and variable andG for Bianchi-type universes are studied under the assumption of a power-law time variation of the expansion factor, achieved via a suitable power-law assumption for the Hubble parameter suggested by M. S. Berman. All the models have a power-law variation of pressure and density and are singular at the epocht=0. The variation ofG(t) as 1/t and (t) as 1/t ² is consistent with these models.     

Sb modified Fe–Mn/TiO<Subscript>2</Subscript> catalyst for the reduction of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> with NH<Subscript>3</Subscript> at low temperatures

Manganese-based catalysts have attracted much attention due to their excellent performance for NO reduction with NH₃ (NH₃-SCR) at low temperatures. In the current study, the novel metal Sb was modified into Mn/TiO₂ and Fe–Mn/TiO₂, and the NO _x conversion was compared with those of Mn/TiO₂ and Fe–Mn/TiO₂ catalysts to investigate the effect of the Sb. The NO _x reduction activities of the catalysts were evaluated in the temperature range of 100–250 °C at a space velocity of 60,000 h^?1. The physicochemical properties of all the catalysts were characterized by Brunauer–Emmett–Teller surface area, temperature-programmed desorption of ammonia, temperature-programmed reduction, X-ray photoelectron spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy. Interestingly, the Sb-promoted Mn-based catalysts showed significantly higher NO _x conversion than the other catalysts with or without 6 vol% of H₂O. The high performance of the Sb-modified catalysts could be related to the increase of acid sites and redox properties.     

Optimization of salt concentration and explanation of two peak percolation in blend solid polymer nanocomposite films

The present paper is focused toward the preparation of the flexible and free-standing blend solid polymer electrolyte films based on PEO-PVP complexed with NaPF₆ by the solution cast technique. The structural/morphological features of the synthesized polymer nanocomposite films have been investigated in detail using X-ray diffraction, Fourier transform infra-red spectroscopy, Field emission scanning electron microscope, and Atomic force microscopy techniques. The film PEO-PVP?+?NaPF₆ (\( \ddot{\mathrm{O}}/{\mathrm{Na}}^{+}= \)8) exhibits highest ionic conductivity ~?5.92?×?10^?6 S cm^?1 at 40 °C and ~?2.46?×?10^?4 S cm^?1 at 100 °C. The temperature-dependent conductivity shows an Arrhenius type behavior and activation energy decreases with the addition of salt. The high temperature (100 °C) conductivity monitoring is done for the optimized PEO-PVP?+?NaPF₆ (\( \ddot{\mathrm{O}}/{\mathrm{Na}}^{+}= \)8) highly conductive system and the conductivity is still maintained stable up to 160 h (approx. 7 days). The thermal transitions parameters were measured by the differential scanning calorimetry (DSC) measurements. The prepared polymer electrolyte film displays the smoother surface on addition of salt and a thermal stability up to 300 °C. The ion transference number (t_ion) for the highest conducting sample is found to be 0.997 and evidence that the present system is ion dominating with negligible electron contribution. Both linear sweep voltammetry and cyclic voltammetry supports the use of prepared polymer electrolyte with long-term cycle stability and thermal stability for the solid-state sodium ion batteries. Finally, a two peak percolation mechanism has been proposed on the basis of experimental findings.

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Graphical abstract A plot of free ion & ion pair area against salt content and AFM image of optimised system

     

Cu2+-driven metallo-supramolecular self-assembly and its application in sensing of hydroxyl ion

The dinuclear copper complex receptor (R) was synthesized using the ligands 4-(di-ethyl-amino)-2-hydroxybenzaldehyde and benzo [d] thiazol-2-amine. The single crystal X-ray analysis of the homoleptic bis(μ-oxo)dicopper (II) complex indicated that the ligands are coordinated in an anti-configuration to each other and have adopted a distorted square-pyramidal environment around the Cu²⁺ ion. The X-ray solid state structural analysis and DFT reveals no direct Cu…..Cu linkage within the complex. The anion recognition ability of the R was studied by UV–vis and fluorescence spectroscopic in acetonitrile. The results indicated that the new complex R displays a sturdy sympathy and selectivity for hydroxide ion.     

Dispersion of resistivity anomalies in critical binary liquid systems

The critical resistivity in the binary liquid systems n-C₇H₁₆ + CH₃OH and CS₂ + CH₃NO₂ is measured from 10 Hz to 100 kHz. There is no noticeable effect of the frequency on the resistivity singularities. Thus any contribution from dielectric dispersion is not appreciable.     

Systematic error in automated in-tube solid-phase microextraction

The widely employed configuration for automated in-tube solid-phase microextraction (SPME) involves modification of a commercial liquid chromatographic autosampler into an automated extraction device. This popular configuration is demonstrated to result in an inherent systematic error in the quantitation of analyte in a given matrix. The source of error is traced to the accumulation of analyte in the extraction and the pre-extraction segment (i.e., sample loop, metering valve and tubing prior to the metering valve) of the autosampler where the analyte comes in contact with the residual mobile phase. This results in cross-contamination due to sample/mobile phase mixing. The quantity of analyte accumulated in these segments is shown to consistently increase with the increasing number of draw/eject cycles. As a result of the accumulation, the amount of analyte recorded leads to inaccurate quantitative information, leading to overestimation of the limit of detection and limit of quantitation, when automated in-tube SPME is employed as an approach for sample enrichment. Insertion of a 100-microl air plug prior to extraction step was able to significantly minimize sample/mobile phase mixing of analyte with the residual mobile phase in the pre-extraction and extraction step, thus minimizing the systematic error.     

Isopiestic Osmotic Coefficients of Tetra-n-methylammonium Chloride with Guanidinium Salts at 298.15 K

Isopiestic osmotic coefficients are presented for aqueous mixtures of tetra-n-methylammonium chloride, (CH₃)₄NCl, with guanidinium salts such as GnCl, CH₃COOGn, GnNO₃, GnClO₄ and Gn₂SO₄ at 298.15 K up to an ionic strength of 2 mol?kg^?1. The osmotic coefficients are analyzed in terms of the Scatchard-Rush-Johnson equations. The activity coefficients of each electrolyte in the mixtures were calculated and fitted by the Harned-type equations. The molar excess Gibbs energy of mixing, Δ_m G ^E, of the mixtures were analyzed with Friedman’s equations.     

The crystal structure of t-Bu2Si(OH)F. A cyclic hydrogen-bonded tetramer

An X-ray diffraction study has shown that t-Bu₂Si(OH)F crystallizes as hydrogen-bonded tetramers. The fluoride ligand does not take part in the hydrogen bonding, which involves OH--O linkages with an OH--O angle of 160°; the O---O---O angles are 89.7(3)°, but the four oxygen atoms are not quite coplanar (space group I$\text{4}$). The t-BuSiBu-t angle is 120.5(6)°.     

BATHOCHROMICITY OF RETINAL SCHIFF BASES IN CELLULOSE MATRIX

Abstract Schiff bases of all-trans-retinal (formed with n-butylamine, tryptamine and β-naphthylamine) and of benzaldehyde, trans -cinnamaldehyde and all- trans -retinal with aniline exhibit an appreciable red shift in their UV-visible maxima on intercalation in cellulose matrix relative to their absorption in solution in the absence of acid. Treatment of these model compounds with trichloroacetic acid in solution gives the corresponding protonated salts. The red shift due to the cellulose environment is, however, less than the red shift in acid solutions. However, an exception is all- trans-N -retinylidenetryptamine for which the red shift in cellulose is quite close to the corresponding value for the protonated salt in heptane and methanol. N -Benzalideneaniline and trans- N -cinnamalideneaniline, with shorter polyenic moieties, tend to show a greater bathochromic shift in cellulose. all-trans- N -Retinylidene- n -butylamine, all- trans-N -retinylidenetryptamine and all- trans-N -retinylidene-β-naphthylamine show a reduced bathochromic shift when intercalated in cellulose pretreated with a base such as n -butylamine. The chromophore of all- trans-N -retinylidenetryptamine is stabilized by the presence of the indole moiety. These results indicate the importance of hydrogen-bond interactions at the chromophore sites of rhodopsins. A mechanistic proposal for explaining protonation, stability and wavelength regulation in the opsin family of proteins is discussed.     

Synthesis of 4,4-dimethyl-3,4-dihydro-3,3,5-trisubstituted-2H-pyrazoles and N-benzoyl derivatives: Method for “Hydrolysis” of unreactive amides and carbamates

Addition of organolithium reagents to 4,4-dimethyl-3,5-disubstituted-4H-pyrazoles produced a series of 4,4-dimethyl-3,4-dihydro-3,3,5-trisubstituted-2H-pyrazoles, 2–6 , in good yield. The reaction was stereoselective: addition of organolithium compounds occurred only to carbon-3 of 4,4-dimethyl-3-alkyl-5-aryl-4H-pyrazoles. The 3,4-dihydro-2H-pyrazoles were found to be of high sensitivity to oxygen. For long term storage and ease of handling, N-benzoyl derivatives were synthesized. Removal of the protecting group could not be accomplished by use of many standard sets of conditions. Deprotection was accomplished in high yield by reaction of the N-benzoyl-4,4-dimethyl-3,4-dihydro-3,3,5-trisubstituted-2H-pyrazoles with anhydrous potassium t-butoxide in toluene [heated under reflux (ultra-pure argon)] in the presence of a phase transfer catalyst (18-Crown-6). Cleavage of a N-carbamate derivative was also achieved by this phase transfer approach. This methodology should be applicable to the hydrolysis of unreactive amides and carbamates in general.