Homology of GL<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>: injectivity conjecture for GL<Subscript>4</Subscript>

The homology of GL _n (R) and SL _n (R) is studied, where R is a commutative ‘ring with many units’. Our main theorem states that the natural map H ₄(GL₃(R), k) → H ₄(GL₄(R), k) is injective, where k is a field with char(k) ≠ 2, 3. For an algebraically closed field F, we prove a better result, namely, is injective. We will prove a similar result replacing GL by SL. This is used to investigate the indecomposable part of the K-group K ₄(R).     

Microwave‐promoted oxidation of 1,3,5‐trisubstituted 4,5‐dihydro‐1H‐pyrazoles by in‐situ generation of NO+ and NO respectively from sodium nitrite and sodium nitrate in acetic acid

Microwave‐assisted aromatization of 1,3,5‐trisubstituted 4,5‐dihydro‐1H‐pyrazoles by in‐situ generation of NO⁺ and NO₂⁺ respectively from sodium nitrite and sodium nitrate in acetic acid has been carried out efficiently under mild reaction conditions in good to excellent yields.     

Biginelli reaction for synthesis of novel trifluoromethyl derivatives of bis(tetrahydropyrimidinone)benzenes

A facile one-pot three-component condensation of terephthalic aldehyde with urea and fluorinated 1,3-dicarbonyl derivatives is developed using catalytic quantities of chlorotrimethylsilane at ambient temperature. As a consequence, efficient synthesis of novel trifluoromethyl derivatives of bis(tetrahydropyrimidinone)benzenes is observed within short time periods. The procedure is shown to be equally efficient when urea is replaced with thiourea or guanidine.     

Magnetic solid-phase extraction of warfarin and gemfibrozil in biological samples using polydopamine-coated magnetic nanoparticles via core-shell nanostructure

Herein, polydopamine-coated Fe₃O₄ spheres were synthesized using a very simple, easy, cost-effective, efficient, and fast method. First, magnetic nanoparticles (Fe₃O₄) were synthesized and were followed by accommodating polydopamine on the surface of the prepared Fe₃O₄. The prepared polydopamine-coated Fe₃O₄ spheres were utilized as a sorbent in magnetic solid phase extraction of gemfibrozil and warfarin (as the model analytes). The extracted model analytes were desorbed by a suitable organic solvent and were analyzed by high-performance liquid chromatography. Under optimized condition, the linearity of the method was in the range of 0.1–200.0 μg/L for the selected analytes in water. The limits of detection were calculated to be in the range of 0.026–0.055 μg/L for warfarin and gemfibrozil, respectively. The limits of quantification were calculated to be in the range of 0.089–0.185 μg/L. The inter-day and intra-day relative standard deviations were determined to be in the range of 1.4%–3.3% in three concentrations in order to calculate the method precision. Furthermore, the enrichment factors were found to be 78 and 81 for warfarin and gemfibrozil, respectively. Moreover, the calculated absolute recoveries were between 78% and 81%. The obtained recoveries indicated that the method was useful and applicable in complicated real samples.     

Volumetric Properties of Tetra-n-butyl ammonium bromide in Aqueous Solutions of Magnesium sulphate in the Temperature Range 298.15 to 318.15K and under the Atmospheric Pressure

Density and sound speed measurements have been carried out for the ternary systems consisting of tetra-n-butyl ammonium bromide (TBAB) in 0.1 m aqueous magnesium sulphate heptahydrate (MgSO₄.7H₂O)-water over the full range of composition from T = 293.15 to 318.15 K by using volumetric method. Using this experimental data, various physical and thermodynamical parameters such as adiabatic compressibility, apparent molal compressibility, apparent molal volume, apparent and limiting partial molar volumes of the electrolytes and ions in these mixtures have been evaluated and split into respective ionic contributions. The results have been discussed in terms of ion–ion and ion–solvent interactions occurring between TBAB and aqueous MgSO₄ solutions. Further, structure making/breaking behaviour of MgSO4 has been reported in terms of sign of the partial molar expansibility at infinite dilution.     

Vibrational and configurational heat capacity of poly(vinyl acetate) from dynamic measurements

The complex heat capacity C(p) (*) of poly(vinyl acetate) has been measured at 20.95 mrads modulation frequency during the cooling as well as on heating at 24, 8, and 2 Kh and during cooling at 0.5 Kh. The study is complemented with (the rate-dependent) C(p,app) measured during cooling and heating at 60, 24, and 8 Kh. At low temperatures, the real component of C(p) (*) yields the unrelaxed C(p) or C(p,vib), the vibrational part of C(p). It is found to be indistinguishable from C(p,glass) and lies on a line extrapolated to its equilibrium melt's temperature. At T near T(g),DeltaC(p)(=C(p,melt)-C(p,glass)) shows no detectable contribution from C(p,vib). The finding conflicts with a modified entropy theory calculation [E. A. DiMarzio and F. Dowell, J. Appl. Phys. 50, 6061 (1979)], which had predicted that approximately 27% of DeltaC(p) of poly(vinyl acetate) at T near T(g) is vibrational in origin and the remainder configurational. At T相似文献   

Determining vibrational heat capacity and thermal expansivity and their change at glass-liquid transition

The vibrational parts of a liquid's heat capacity Cp and thermal expansion coefficient alpha may be determined from dynamic measurements. The Cp data for Pd40Ni40P20 and 0.4 Ca(NO3)(2).0.6 KNO3 have been analyzed accordingly, and it is found that change in the vibrational part at liquid-glass transformation is negligible. Analysis for alpha of poly(styrene) leads to the same conclusion. There is no discontinuity in the vibrational parts of Cp and alpha on structural unfreezing in the Tg range, and hence the change in Cp and alpha at Tg is almost entirely due to change in the configurational part. Crystallization decreases the vibrational part not because the molecular mobility is lost but because the density increases.     

Composition dependence and the nature of endothermic freezing and exothermic melting

The heat capacity, C(p), and enthalpy and entropy change of alpha-cyclodextrin, H(2)O, and 4-methylpyridine solutions have been studied during their freezing on heating, isothermal freezing, and the solid's melting on cooling. Freezing occurs in several endothermic steps on heating to 383 K and alpha-cyclodextrin rich solutions freeze in four steps. The melting rate becomes slower with decrease in temperature and its steps merge. Decreasing the amount of alpha-cyclodextrin decreases the C(p) change on freezing. The endothermic freezing phenomenon differs from freezing of a pure liquid and is attributed to formation of a solid inclusion compound and its incongruent way of exothermic melting.     

Dielectric spectroscopy and calorimetry during postcuring of a linear chain polymer thermoset formed from a diepoxide and cyclohexylamine,and the nature of the products

The dielectric permittivity and loss spectra of an equimolar liquid mixture of diglycidyl ether of bisphenol-A and cyclohexylamine have been studied during the liquid's isothermal polymerization or curing in separate experiments at different temperatures and thereafter during the postcuring, both on rate-heating and isothermally. The spectra obtained during the growth of the linear chain polymer during the curing and postcuring show the evolution of an intermediate relaxation process whose position in the frequency plane remains relatively insensitive to the decrease in the configurational entropy during the postcuring, but whose strength increases. Postcuring ceases to occur once the calorimetric glass-liquid transition temperature of 345 K, corresponding to the ultimately formed polymeric state, has been reached. The increase in the number of covalent bonds, n, formed during curing and postcuring decreased the equilibrium dielectric permittivity, ε_s, and increased the characteristic relaxation time, τ₀, for all curing and postcuring conditions. For a fixed temperature and n, (dε_s/dT) and (dτ₀/dT), as well as the values ε_s and τ₀ of the ultimately formed state of the polymers differ significantly when the thermal history of polymerization differs. The slow dynamics in the glass-liquid transition region were analyzed in terms of the enthalpy relaxation and fictive temperature concepts. The distribution of relaxation times for these dynamics correspond to the stretched exponential parameter of 0.6, which is significantly greater than 0.39 determined for the dielectric α-relaxation spectra measured at a temperature 30 K higher. The enthalpy relaxation involves a narrower distribution of intermolecular barriers than dielectric relaxation. The results also show that the recently proposed method for determining the gelation time from the plots of the imaginary component of electrical impedance lacks scientific merit. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 303–318, 1998     

Calorimetric and dielectric effects during polymerization of an elastomer‐containing mixture and liquid‐liquid phase separation

Calorimetry and dielectric spectroscopy of an elastomer, amine terminated butadiene acrylonitrile (ATBN), dissolved in a stoichiometric mixture of ethylene diamine and diglycidyl ether of bisphenol‐A, were studied in real time during the polymerization and phase separation of the mixture. In the two polymer compositions containing 8 w/w % ATBN and 20 w/w % ATBN, the total enthalpy released per mole of DGEBA's reaction was the same, indicating indetectably small changes in molecular interactions before and after the phase separation. The dielectric relaxation spectra showed no evidence for phase separation, which indicated a gradual phase separation with time and the extent of polymerization, and relatively small differences in the permittivity and conductivity between the ATBN particles and the network matrix at the time of phase separation. The equilibrium permittivity and dc conductivity showed a nonideal mixing of ATBN. The stretched exponential relaxation parameter remained at 0.36, but the characteristic dielectric relaxation time and the dc conductivity increased on addition of ATBN. An increase in the temperature had a greater effect on the relaxation time than the increase in the extent of polymerization. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1911–1919, 1999