Rheological behaviour of polyoxometalate-doped lyotropic lamellar phases

We study the influence of nanoparticle doping on the lyotropic liquid crystalline phase of the industrial surfactant Brij30 ( C₁₂E₄ and water, doped with spherical polyoxometalate nanoparticles smaller than the characteristic dimensions of the host lamellar phase. We present viscometry and in situ rheology coupled with small-angle X-ray scattering data that show that, with increasing doping concentration, the nanoparticles act to decrease the shear viscosity of the lamellar phase, and that a shear-induced transition to a multilamellar vesicle “onion” phase is pushed to higher shear rates, and in some cases completely suppressed. X-ray data reveal that the nanoparticles remain encapsulated within the membranes of the vesicles, thus indicating a viable method for the fabrication of nanoparticle incorporating organic vesicles.     

Loss enhanced phase locking in coupled oscillators

Phase locking, which is achieved by transferring some energy from one oscillator to the others, strongly depends on the coupling strength between the oscillators. Typically, the coupling strength must be above a certain threshold in order to achieve phase locking. Here we show how this threshold can be significantly reduced when phase-dependent losses are introduced into the oscillators. Specifically, the coupling strength can be reduced by at least an order of magnitude, thereby substantially decreasing the needed transfer of energy between oscillators. The resulting enhancement of phase locking does not only influence the laser research area, but also affects many other areas that involve coupled ensembles.     

On the character of three 8+ states in 192Pb

Three low-lying 8⁺ states have been identified in ¹⁹²Pb . A newly observed cascade of $ \gamma$ -rays built directly on the 8⁺ ₁ state is compared to the previously identified, weakly rotational band above the 11^- $ \pi$ i _13/2 , h _9/2 isomer in the same nucleus, and to analogous structures in ¹⁹⁴Pb . The similarity of all four structures lends support to the suggestion that the 8⁺ ₁ configurations are of a similar oblate deformation to the 11^- isomers. The excitation energies of all three 8⁺ states in ¹⁹²Pb and ¹⁹⁰Pb are compared to systematics. The possibility that one of the 8⁺ states in ¹⁹²Pb is associated with a prolate shape is discounted.     

Measuring magnetic profiles at manganite surfaces with monolayer resolution

The performance of manganite-based magnetic tunnel junctions (MTJs) has suffered from reduced magnetization present at the junction interfaces that is ultimately responsible for the spin polarization of injected currents; this behavior has been attributed to a magnetic “dead layer” that typically extends a few unit cells into the manganite. X-ray magnetic scattering in resonant conditions (XRMS) is one of the most innovative and effective techniques to extract surface or interfacial magnetization profiles with subnanometer resolution, and has only recently been applied to oxide heterostructures. Here we present our approach to characterizing the surface and interfacial magnetization of such heterostructures using the XRMS technique, conducted at the BEAR beamline (Elettra synchrotron, Trieste). Measurements were carried out in specular reflectivity geometry, switching the left/right elliptical polarization of light as well as the magnetization direction in the scattering plane. Spectra were collected across the Mn L_2,3 edge for at least four different grazing angles to better analyse the interference phenomena. The resulting reflectivity spectra have been carefully fit to obtain the magnetization profiles, minimizing the number of free parameters as much as possible. Optical constants of the samples (real and imaginary part of the refractive index) in the interested frequency range are obtained through absorption measurements in two magnetization states and subsequent Kramers–Krönig transformation, allowing quantitative fits of the magnetization profile at different temperatures. We apply this method to the study of air-exposed surfaces of epitaxial La_2/3Sr_1/3MnO₃ (0 0 1) films grown on SrTiO₃ (0 0 1) substrates.     

Ab initio calculations on XFnq (X = I,Xe, Cs,and Ba; n=1, 2, 4, and 6; q=−1, 0, +1, and +2) molecules

Ab initio calculations employing relativistic effective core potentials were carried out to investigate the electronic structure of xenon fluoride molecules. The chemical bonds and geometrical stability of some isoelectronic ions, which have the central atom replaced by iodine, cesium, and barium ions, were also investigated. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 238–245, 2001     

A shock tube study of the pyrolysis of NO2

NO₂ concentration profiles in shock-heated NO₂/Ar mixtures were measured in the temperature range of 1350–2100 K and pressures up to 380 atm using Ar⁺ laser absorption at 472.7 nm, IR emission at 6.25±0.25 μm, and visible emission at 300–600 nm. In the course of this study, the absorption coefficient of NO₂ at 472.7 nm was measured at temperatures from 300 K to 2100 K and pressures up to 75 atm. Rate coefficients for the reactions NO₂+M→NO+O+M (1), NO₂+NO₂→2NO+O₂ (2a), and NO₂+NO₂→NO₃+NO (2b) were derived by comparing the measured and calculated NO₂ profiles. For reaction (1), the following low- and high-pressure limiting rate coefficients were inferred which describe the measured fall-off curves in Lindemann form within 15% [FORMULA] The inferred rate coefficient at the low- pressure limit, k_1o, is in good agreement with previous work at higher temperatures, but the energy of activation is lower by 20 kJ/mol than reported previously. The pressure dependence of k₁ observed in the earlier work of Troe [1] was confirmed. The rate coefficient inferred for the high pressure limit, k_1∞, is higher by a factor of two than Troe's value, but in agreement with data obtained by measuring specific energy-dependent rate coefficients. For the reactions (2a) and (2b), least-squares fits of the present data lead to the following Arrhenius expressions: [FORMULA] For reaction (2), the new data agree with previously recommended values of k_2a and k_2b, although the present study suggests a slightly higher preexponential factor for k_2a. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 483–493, 1997.     

Does Urea Preferentially Interact with Amide Moieties or Nonpolar Sidechains? A Question Answered Through a Judicious Selection of Model Systems

The transfer model suggests that urea unfolds proteins mainly by increasing the solubility of the amide backbone, probably through urea-induced increase in hydrogen bonding. Other studies suggest that urea addition increases the magnitude of solvent-solute van der Waals interactions, which increases the solubility of nonpolar sidechains. More recent analyses hypothesize that urea has a similar effect in increasing the solubility of backbone and sidechain groups. In this work, we compare the effects of urea addition on the solvation of amides and alkyl groups. At first, we study the effects of urea addition upon solvent hydrogen bonding acidity and basicity through the perturbation in the fluorescence spectrum of probes 1-AN and 1-DMAN. Our results demonstrate that the solvent's hydrogen bonding properties are minimally affected by urea addition. Subsequently, we show that urea addition does not perturb the intra-molecular hydrogen bonding in salicylic acid significantly. Finally, we investigate how urea preferentially interacts with amide and alkyl groups moieties in water by comparing the effects of urea addition upon the solubility of acetaminophen and 4-tertbutylphenol. We show that urea affects amide and t-butyl solubility (lowers the transfer free energy of both amide (backbone) and alkyl (sidechain) groups) in a similar fashion. In other words, preferential interaction of urea with both moieties contributes to protein denaturation.