On the open immersion problem

We give two examples of complex spaces on which global holomorphic functions separate points and give local coordinates and they cannot be realized as open subsets of Stein spaces. At the same time we notice that these examples are open subsets of Stein schemes, a notion introduced by Grauert (Math Z 81:377–391, 1963). In the context of complex schemes we notice that by contracting a Nori string one obtains a complex scheme and not a complex space. The covering spaces of 1-convex surfaces are divided in two categories: those that have an envelope of holomorphy and those that do not. More interesting are those in the second category and they correspond to covering spaces for singularities which in the desingularization with normal crossings contain cycles in the exceptional set.     

BaVS3 probed by V L edge x-ray absorption spectroscopy

Polarization dependent vanadium L edge x-ray absorption spectra of BaVS(3) single crystals are measured in the four phases of the compound. The difference between signals with the polarizations E perpendicular to c and E is parallel to c (linear dichroism) changes with temperature. Besides increasing the intensity of one of the maxima, a new structure appears in the pre-edge region below the metal-insulator transition. More careful examination brings to light that the changes start already with pretransitional charge density wave fluctuations. Simple symmetry analysis suggests that the effect is related to rearrangements in the E(g) and A(1g) states, and is compatible with the formation of four inequivalent V-sites along the V-S chain.     

Solvent effect on the syn/anti conformational stability: A comparison between conformational bias Monte Carlo and molecular dynamics methods

The solvent effect on the syn/anti population ratio of the mesityl oxide (MOx) was investigated using a new implementation of conformational bias Monte Carlo (CBMC) and molecular dynamics (MD) methods. It was observed by a previous theoretical work (Theor. Chem. Acc. (2012) 131:1214) that in gas-phase the MOx exists dominantly in syn-form and in aqueous solution in anti-form. The syn/anti free energy difference in the gas phase was used in the intramolecular parametrization and a rotational barrier of approximately 10 kcal mol⁻¹ was found. Molecular systems with barriers of this order of magnitude have been studied by experimental techniques. However, they have not been discussed yet comparing CBMC and MD simulations. In this work, we show that the intramolecular geometrical information such as bond lengths, angles and torsional angles sampled with CBMC and MD methods are equivalent. Nonetheless, only the CBMC simulations sample appropriately the syn/anti population ratio. With the CBMC configurations in gas phase, it was obtained 95% in syn-form and 5% in anti-form regardless the initial conformation. An inversion of the population was found in water, 25% in syn-form and 75% in anti-form. Comparing the gas phase and in-water CBMC sampling, it was observed that the MOx spends typically approximately 110 successive MC cycles in anti-form and approximately 2300 in syn-form in gas phase. While it was much larger with explicit water, approximately 400 times more for anti-form and approximately 6 times more for syn-form. We argue that this strong stabilization of the anti-form in aqueous solution, does not come from the MOx-water hydrogen bonds interactions, because they are the same for both conformations. Instead, the stabilization comes from the dipole-dipole interaction caused by a larger dipole moment of the MOx in the anti-form, 7.2 D, than in the syn-form, 5.2 D. With the MD sampled configurations in both conditions, we observe that the syn/anti conformational change is a very rare event due to the rotational barrier, which is approximately 17 times larger than the thermal energy. Therefore, the MD sampling of the MOx is not appropriated because it is strongly dependent on the initial conformation even for large simulations with 150 ns up to 400 ns for the isolated solute and for solute–solvent systems.     

Structural evolution of Co clusters on Cu90Co10 upon annealing

A granular alloy, composed of cobalt embedded in a copper matrix, was studied by using EXAFS and magnetotransport measurements as function of annealing parameters (temperature and annealing time). The results suggest that different annealing routes can reach the same final state. For annealing temperatures up to 450°C, the results indicate the coalescence of cobalt atoms, resulting in magnetic particles with increasing size. On the other hand, the annealing at 500°C shows a rapid formation of cobalt particles and then the re-dissolution of cobalt atoms in the copper matrix.     

Organo-modified cationic silica nanoparticles/anionic polymer as flocculants

The synthesis of quaternized silica nanoparticles and its application to fine clay flocculation were investigated. N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride was used as a cationic reagent to introduce quaternary amine groups onto the surfaces of silica nanoparticles via the formation of covalent bonds between the methoxy groups of the cationic reagents and the silanol groups in the silica surface. The zeta potential, zeta, and charge density of the silica particles modified under various reaction conditions were determined. Dynamic clay flocculation experiments using a photometric dispersion analyzer (PDA) showed that the cationic silica alone contributed little to the flocculation. However, the cationic silica, in conjunction with an anionic polymer of high M(w) and low charge density, led to a significant improvement in the flocculation of fine clay particles. The mechanism of flocculation was explored by a systematic investigation of interaction between cationic silica and anionic polymers as well as of their adsorption behavior on clay surfaces. The influence of factors such as pH and electrolyte concentration on clay flocculation was also investigated.     

Efficient and practical catalytic vinylogous aldol reaction of dioxinone-derived silyl dienol ethers with aromatic aldehydes

Vinylogous Mukaiyama-aldol reaction was realized by use of dioxinone-derived silyl dienol ethers and various aldehydes in the presence of highly catalytic amounts of bismuth triflate. The reaction proceeds rapidly and affords the corresponding β-hydroxy-1,3-dioxin-4-ones in very good to excellent yields (up to 98%).     

Cationic-modified cyclodextrin nanosphere/anionic polymer as flocculation/sorption systems

Simultaneous removal of dissolved and colloidal substances has been a challenging task. The cationic-modified beta-cyclodextrin nanospheres synthesized in this work, in conjunction with a water-soluble polyacrylamide-based anionic polymer, potentially provide a novel approach to address the problem. The cyclodextrin was rendered cationic using (2,3-epoxypropyl)trimethylammonium chloride as a reagent. The cationicity of the modified cyclodextrin and the reaction between cyclodextrin and the reagent were characterized by electrophoresis measurement, polyelectrolyte titration, and NMR. As a dual-component flocculation system, the cationic cyclodextrin/anionic polymer significantly induced clay flocculation, lowering the relative turbidity of the clay suspension over a wide pH range. Meanwhile, as a nanospherical absorbent, the modified cyclodextrins exhibited strong affinity toward aromatic compounds via inclusion complex formation in the hydrophobic cavities, which was monitored by UV spectroscopy. These systems facilitated the simultaneous removal of dissolved and colloidal substances, which was unachievable previously. In addition, the interaction between anionic polymers and the clay particles pretreated with cationic cyclodextrin was investigated in order to reveal the flocculation mechanism.     

Cocrystallization in ternary blends of ferroelectric copolymers

In this work, we report evidences of cocrystallization in ternary blends made of crystalline ferroelectric poly(vinylidene fluoride‐trifluorethylene) [P(VDF‐TrFE)] copolymers. Complete cocrystallization has been unequivocally demonstrated by the observation of just one Curie and one Melting temperature in their calorimetric thermograms. These temperatures were intermediary among the respective temperatures of the individual constituents, that is, P(VDF‐TrFE)_72/28, P(VDF‐TrFE)_63/37, and P(VDF‐TrFE)_50/50. Dielectric and X ray diffraction data were used to complement the investigation. The binary blends made of 63/37 and 72/28 copolymers were found to be miscible in the entire range of composition, with the behavior of their Curie temperatures being well fitted by an equation very similar to that proposed by Gordon‐Taylor to describe the behavior of the glass transition temperatures in true binary blends. In the ternary crystalline system, we have found evidences that the complete miscibility of the binary blend made of 63/37 and 72/28 copolymers actually drives the P(VDF‐TrFE)_50/50 copolymer to accommodate their chains in its binary crystalline structure. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 621–626, 2010     

Iodine determination in food by inductively coupled plasma mass spectrometry after digestion by microwave-induced combustion

Iodine determination in food samples was performed by inductively coupled plasma mass spectrometry (ICP-MS) after digestion by microwave-induced combustion (MIC). Sample masses up to 500 mg of bovine liver, corn starch, milk powder, or wheat flour were completely combusted using the MIC system. Ammonium nitrate (6 mol l⁻¹ solution, 50 μl) was used as an aid for ignition and vessels were charged with 15 bar of O₂. The use of H₂O, 0.9 mmol l⁻¹ H₂O₂, 10 to 50 mmol l⁻¹ (NH₄)₂CO₃ and 56 mmol l⁻¹ tetramethylammonium hydroxide was investigated as absorbing solutions, as well as the suitability of performing a reflux step after the combustion process. Digestion of food samples by pressurized microwave-assisted acid digestion, microwave-assisted extraction and conventional extraction of iodine in alkaline solution were also evaluated. Iodine recoveries higher than 99% were obtained using MIC and 50 mmol l⁻¹ (NH₄)₂CO₃ or 56 mmol l⁻¹ tetramethylammonium hydroxide as absorbing solution and with 5 min for the reflux step. Accuracy was evaluated using certified reference materials (bovine muscle, corn bran, and milk powder) and agreement better than 97% was obtained. The limit of quantification by MIC and further ICP-MS determination was 0.002 μg g⁻¹. Blanks were always low and no memory effects were observed. Digestion by MIC allowed the processing of up to eight samples by each run in 25 min with high efficiency of digestion (residual carbon content lower than 1%) providing a suitable medium for further iodine determination by ICP-MS.