Complexes between divalent metals and carboxylic acids: Semiempirical study

The possibility to predict the stability constants of the complexes of magnesium, zinc, cadmium, and lead cations with anions of different carboxylic acids by PM3 calculations was investigated. Linear correlation between calculated complex-formation reaction enthalpies and experimentally measured stability constants were obtained for complexes of each metal, while the overall correlation was not satisfactory. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 653–658, 1997     

Homopolymer surfactant for immiscible homopolymer blends

It is commonly believed that block copolymers are the only type of polymeric surfactants available for incompatible homopolymers(¹). We explore the conditions for which a homopolymer will also lower the surface tension between two incompatible homopolymers by lowering the enthalpic contribution to the interfacial free energy, noting that the resulting three-component interface will not necessarily have the same mechanical strength as a block copolymer-homopolymer interface.     

Identification of plastic material parameters with error estimation

In recent years, inverse analysis has become a common approach to typical engineering problems such as model identification. In this contribution, the inverse problem is discussed in light of taking experimental uncertainties into account. This involves in particular the propagation of experimental errors and the analysis of the sensitivity of the model response to variations in the model parameters to be determined. The method is applied to an elasto-viscoplastic material model which is used in the context of electromagnetic high-speed forming. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Where Is a Singer''s Voice if It Is Placed “Forward”?

Singing teachers sometimes characterize voice quality in terms of "forward" and "backward" placement. In view of our traditional knowledge about voice production it is hard to explain any possible acoustic or articulatory differences between the voices so "placed." The analysis of the teachers' expert opinions demonstrates that, in general, a voice placed "forward" indicates a desirable quality that students should attain by the end of their studies. Productions that were perceived as "forward" and "backward" were selected from the listening test. The acoustic analysis of those productions reveals that the voice quality in the case of "forward" placement correlates with higher frequencies of the second (F2) and third (F3) formants, as well as with a more salient "singer's formant" in the voice. The five basic vowels were included in the investigation.     

The perfluorinated alcohols (F5C6)(F3C)2COH and (F5C6)(F10C5)COH: synthesis, theoretical and acidity studies, spectroscopy and structures in the solid state and the gas phase

The syntheses of the perfluorinated alcohols (F(5)C(6))(F(3)C)(2)COH (1) and (F(5)C(6))(C(5)F(10))COH (2) are described. Both compounds were prepared in reasonable yields (1: 65%, 2: 85%) by reacting the corresponding ketone with C(6)F(5)MgBr, followed by acidic work-up. The alcohols were characterized by NMR, vibrational spectroscopy, single-crystal X-ray diffraction, acidity measurements and gas-phase electron diffraction. A combination of appropriate 2D NMR experiments allowed the unambiguous assignment of all signals in the (19)F spin systems, of which that of 2 was especially complex. High acidity of the alcohols is indicated by acidity measurements as well as the calculated gas phase acidities. It is also supported by the crystal structure of 2, which exhibits only a single weak intermolecular hydrogen bridge with an O...O distance of 301 pm. This shows the low donor strength of the oxygen atom in the compound, which is partly compensated through formation of two intramolecular CF...H contacts of 220 and 232 pm length to the proton not involved in the hydrogen bridge. The pK(a) values in acetonitrile are 22.2 for 1 and 22.0 for 2; their calculated gas phase acidities are 1367 and 1343 kJ mol(-1) (MP2/TZVPP level).     

Reaction pathway to Cu2ZnSnSe4 formation in CdI2

Journal of Thermal Analysis and Calorimetry - We investigated various possible chemical interactions between individual precursor compounds (ZnSe, SnSe, and CuSe) and CdI2 as a flux material used...     

Spectra and structure of small ring compounds: Part XXX. Microwave spectrum of 1,1-difluoro-1-silacyclopent-3-ene

The microwave spectrum of 1,1-difluoro-l-silacyclopent-3-ene has been recorded from 26.5 to 40.0 GHz. Only A-type transitions were observed. The R-branch assignments have been made for the ground state and the first three excited states of the ring puckering vibration. It is shown that the five-membered ring structure is planar from the values of the components of the dipole moment, as well as from the value of the inertial defect as a function of the ring puckering quantum number. From the relative intensity measurements, it is concluded that the first excited state of the ring puckering vibration has a frequency of 38 ±7 cm^?1 and that the vibration is nearly harmonic. The components of the dipole moment were determined by the Stark effect to be μ_a = 2.02 ±0.06 D, μ_b = 0, and μ_c = 0.0 ±0.09 D. All of the observed data are consistent with a molecule of C_2v symmetry and the possible reasons for this structure are discussed.     

Concentration and temperature dependence of the refractive index increment of a polystyrene sample in trans-decalin

The refractive index increment of macromolecules in solution has been observed to be a function of concentration, temperature, molecular weight, wavelength of light, and solvent. Most of the studies have been performed in dilute or semidilute solutions, and therefore the concentration dependence of the refractive index increment was too small to be accurately observed. This study was performed on solutions of polystyrene in trans-decalin at mass fractions, w₂, from 0.01 to 0.11 and at 436 and 546 nm wavelengths. The concentration and temperature dependence of the refractive index increment were measured, and comparisons were made with previous theories.     

Sticky particles in compressible flows: aggregation and Richardson's law

The evolution of the distance r(t) between a pair of passive tracer particles in rough compressible velocity fields is studied. The scaling behavior depends on the stickiness of the particles. Sticky particles start aggregating in moderately compressible flows, which can be realized on the free-slip surface of a turbulent fluid; nonsticky particles can aggregate only in less common strongly compressible flows (even then, the aggregation rate remains lower). Aggregation gives rise to an anomalous scaling law for the mean-square-distance growth rate, slower than Richardson's law. These findings help understand the results of recent experiments.