Study of ferrofluids by Mössbauer spectroscopy

The parameters of the log‐normal size distribution of a MnFe₂O₄ ferrofluid powder sample have been determined by X‐ray diffraction. The mean blocking temperature was determined from the maximum of _Xi . Mössbauer spectra at 4.2–300 K are interpreted by a new simple theory of superparamagnetism and taking a reduction of the internal magnetic field for small particles, a size dependence of the anisotropy constant, the size distribution and collective excitations into account.     

Generalized prolate spheroidal wave functions for offset linear canonical transform in Clifford analysis

Prolate spheroidal wave functions (PSWFs) possess many remarkable properties. They are orthogonal basis of both square integrable space of finite interval and the Paley–Wiener space of bandlimited functions on the real line. No other system of classical orthogonal functions is known to obey this unique property. This raises the question of whether they possess these properties in Clifford analysis. The aim of the article is to answer this question and extend the results to more flexible integral transforms, such as offset linear canonical transform. We also illustrate how to use the generalized Clifford PSWFs (for offset Clifford linear canonical transform) we derive to analyze the energy preservation problems. Clifford PSWFs is new in literature and has some consequences that are now under investigation. Copyright © 2012 John Wiley & Sons, Ltd.     

Efficient one-pot synthesis of glycosyl disulfides

Methodology for the efficient and facile synthesis of glycosyl disulfides is reported. A one-pot procedure employing mild conditions using diethyl azodicarboxylate is described to synthesise a series of glycosyl disulfides in excellent yields.     

Dispersing phase viscometry and zeta potential in alumina dispersions

The stabilities of alumina dispersions were studied as a function of poly- and low molecular weight electrolyte concentration, using viscometry of the dispersing phase, and zeta potential measurements. The relation of polyelectrolyte adsorption to polymer concentration (at different low molecular weight electrolyte concentrations) was found to depend upon the dimensions of the polymer (which were a priori known to decrease with increasing poly- and low molecular weight electrolyte concentration). The occurrence of flocculation and bridging in the destabilization mechanism of the alumina dispersions was also characterized.     

DIFFRACTION AND HOLOGRAPHY WITH PHOTOELECTRONS AND FLUORESCENT X-RAYS

We consider studies of the atomic and magnetic structure near surfaces by photoelectron diffraction and by the holographic inversion of both photoelectron diffraction data and diffraction data involving the emission of fluorescent x-rays. The current status of photoelectron diffraction studies of surfaces, interfaces, and other nanostructures is first briefly reviewed, and then several recent developments and proposals for future areas of application are discussed. The application of full-solid-angle diffraction data, together with simultaneous characterization by low energy electron diffraction and scanning tunneling microscopy, to the epitaxial growth of oxides and metals is considered. Several new avenues that are being opened up by third-generation synchrotron radiation sources are also discussed. These include site-resolved photoelectron diffraction from surface and interface atoms, the possibility of time-resolved measurements of surface reactions with chemical-state resolution, and circular dichroism in photoelectron angular distributions from both non-magnetic and magnetic systems. The addition of spin to the photoelectron diffraction measurement is also considered as a method for studying short-range magnetic order, including the measurement of surface magnetic phase transitions. This spin sensitivity can be achieved through either core-level multiplet splittings or circular-polarized excitation of spin-orbit-split levels. The direct imaging of short-range atomic structure by both photoelectron holography and two distinct types of x-ray holography involving fluorescent emission is also discussed. Both photoelectron and x-ray holography have demonstrated the ability to directly determine at least approximate atomic structures in three dimensions. Photoelectron holography with spin resolution may make it possible also to study short-range magnetic order in a holographic fashion. Although much more recent in its first experimental demonstrations, x-ray fluorescence holography should permit deriving more accurate atomic images for a variety of materials, including both surface and bulk regions.     

A flow system with in-line blank correction applied to the spectrophotometric determination of total iron and chromium (VI) in wastewaters

A flow system using the sample as the carrier with a propulsion device located after the detector is presented. This approach allows the correction of the intrinsic color of the sample, as it provides baseline adjustment for each sample. A confluence situated just after the selection valve allows the sample composition to be adjusted for the colorimetric measurement. The developed methodology was applied to the colorimetric determination of total Fe and Cr (VI) in wastewaters at 0.1-6.0 mg L-1 and 0.03-1.0 mg L-1, respectively. RSDs lower than 3% and a sampling rate of approximately 40 h-1 were obtained.     

The enthalpies of formation of o-, m-, and p-benzoquinone: gas-phase ion energetics, combustion calorimetry, and quantum chemical computations combined

Radical anions of o-, m-, and p-benzoquinone were produced in a Fourier transform mass spectrometer by low energy electron attachment or collision-induced dissociation and were differentiated. Classical derivatization experiments also were carried out to authenticate the ortho and meta anions. Gas-phase techniques were used to measure the proton affinities of all three radical anions and the electron affinities of o- and m-benzoquinone. By combining these results in thermodynamic cycles, we derived heats of hydrogenation of o-, m-, and p-benzoquinone (Delta(hyd)H degrees (1o, 1m, and 1p) = 42.8 +/- 4.1, 74.8 +/- 4.1, and 38.5 +/- 3.0 kcal mol(-)(1), respectively) and their heats of formation (Delta(f)H degrees (1o, 1m, and 1p) = -23.1 +/- 4.1, 6.8 +/- 4.1, and -27.7 +/- 3.0 kcal mol(-)(1), respectively). Good accord with the literature value for the para derivative was obtained. Combustion calorimetry and heats of sublimation also were measured for benzil and 3,5-di-tert-butyl-o-benzoquinone. The former heat of formation agreed with previous determinations, while the latter result (Delta(f)H degrees (g) = -73.09 +/- 0.87 kcal mol(-)(1)) was transformed to Delta(f)H degrees (1o) = -18.9 +/- 2.2 kcal mol(-)(1) by removing the effect of the tert-butyl groups via isodesmic reactions. This led to a final value of Delta(f)H degrees (1o) = -21.0 +/- 3.1 kcal mol(-)(1). Additivity was found to work well for m-benzoquinone, but BDE1 and BDE2 for 1,2- and 1,4-dihydroxybenzene differed by a remarkably small 14.1 +/- 4.2 and 23.5 +/- 3.7 kcal mol(-)(1), respectively, indicating that o- and p-benzoquinone should be excellent radical traps.     

Thermochemistry of biphenylcarboxylic and dicarboxylic acids. A combined experimental and theoretical study

The standard molar enthalpies of combustion and sublimation of 2- and 4-biphenylcarboxylic acid, 2,2'- and 4,4'-biphenyldicarboxylic acid were measured and the gas-phase enthalpies of formation, at T= 298.15 K, were determined. Ab initio calculations were performed and a theoretical study on molecular structure of all the biphenyl acid isomers has been carried out. Calculated enthalpies of formation using appropriate isodesmic reactions are compared with experimental values, and a good agreement is observed. Estimates of enthalpies of formation for the isomers, which were not studied experimentally, are presented. All the acids containing at least one ortho COOH are comparatively less stable than their isomers having just meta or para COOH group(s).     

Thermodynamic study of sesamol, piperonyl alcohol, piperonylic acid and homopiperonylic acid: a combined experimental and theoretical investigation

The standard (p(o)= 0.1 MPa) molar energies of combustion in oxygen, at T= 298.15 K, of four 1,3-benzodioxole derivatives (sesamol, piperonyl alcohol, piperonylic acid and homopiperonylic acid) were measured by static bomb calorimetry. The values of the standard molar enthalpies of sublimation, at T= 298.15 K, were derived from vapour pressure-temperature measurements using the Knudsen effusion technique. Combining these results the standard molar enthalpies of formation of the compounds, in the gas phase, at T= 298.15 K, have been calculated: sesamol (-325.7 +/- 1.9) kJ mol(-1); piperonyl alcohol (-329.0 +/- 2.0) kJ mol(-1); piperonylic acid (-528.9 +/- 2.6) kJ mol(-1) and homopiperonylic acid (-544.5 +/- 2.9) kJ mol(-1). The most stable geometries of all the compounds were obtained using the density functional theory with the B3LYP functional and two basis sets: 6-31G** and 6-311G**. The nonplanarity of the molecules was analyzed in terms of the anomeric effect, which is believed to arise from the interaction between a nonbonded oxygen p orbital and the empty orbital sigma*(CO) involving the other oxygen atom. Calculations were performed to obtain estimates of the enthalpies of formation of all the benzodioxoles using appropriate isodesmic reactions. There is a perfect agreement between theoretical and experimental results.     

DTG-DTA study of sewage sludge used in the sorption of Cd2+ and Co2+

The present study was carried out for evaluating the retention behavior of sanitary sewage in relation to cadmium and cobalt ions in an ascendant continuous-flow reactor. It was found that the studied sludge presented a high assimilation of the metals, probably due to the presence of anionic groups, which favors adsorption and complexation processes. Thermal analyses of the samples showed a shift in the thermal decomposition of the ‘in natura’ sludge, when compared with those of the samples spiked with the metals, confirming the possibility of interactions between the heavy metals and the anionic groups present in the sludge.