Dzyaloshinsky-Moriya anisotropy in the spin-1/2 kagome compound ZnCu3(OH)6Cl2

We report the determination of the Dzyaloshinsky-Moriya interaction, the dominant magnetic anisotropy term in the kagome spin-1/2 compound ZnCu3(OH)6Cl2. Based on the analysis of the high-temperature electron spin resonance (ESR) spectra, we find its main component |Dz|=15(1) K to be perpendicular to the kagome planes. Through the temperature dependent ESR linewidth, we observe a building up of nearest-neighbor spin-spin correlations below approximately 150 K.     

Altering the crystal morphology of silicalite-1 through microemulsion-based synthesis

The crystal morphology of silicalite-1 was adjusted through a microemulsion-based hydrothermal synthesis. The surfactant cetyltrimethylammonium bromide (CTAB) with cosurfactant butanol was used to form water-in-oil microemulsions containing the silicalite-1 synthesis gel. The crystal morphology of silicalite-1 was adjusted from coffin-shaped to novel rod-shaped and to irregular-shaped nanoparticles by varying the microemulsion composition. Silicalite-1 synthesized in the microemulsion has a smaller size and a more narrow size distribution than that produced by conventional synthesis without the microemulsion. The novel morphology of silicalite-1 may facilitate assembly into films and find applications in separation and catalysis.     

Picosecond time-resolved X-ray absorption spectroscopy of ultrafast aluminum plasmas

We have used point-projection K-shell absorption spectroscopy to infer the ionization and recombination dynamics of transient aluminum plasmas. Two femtosecond beams of the 100 TW laser at the LULI facility were used to produce an aluminum plasma on a thin aluminum foil (83 or 50 nm), and a picosecond x-ray backlighter source. The short-pulse backlighter probed the aluminum plasma at different times by adjusting the delay between the two femtosecond driving beams. Absorption x-ray spectra at early times are characteristic of a dense and rather homogeneous plasma. Collisional-radiative atomic physics coupled with hydrodynamic simulations reproduce fairly well the measured average ionization as a function of time.     

A chiral granular gas

Inspired by rattleback toys, we created small chiral wires that rotate in a preferred direction on a vertically oscillating platform and quantified their motion with experiment and simulation. We demonstrate experimentally that angular momentum of rotation about particle centers of mass is converted to collective angular momentum of center-of-mass motion in a granular gas of these wires, and we introduce a continuum model that explains our observations.     

Spatial uniformity of laser-accelerated ultrahigh-current MeV electron propagation in metals and insulators

The evolution of laser-generated MeV, MA electron beams propagating through conductors and insulators has been studied by comparing measurement and modeling of the distribution of MeV protons that are sheath accelerated by the propagated electrons. We find that electron flow through metals is uniform and can be laser imprinted, whereas propagation through insulators induces spatial disruption of the fast electrons. Agreement is found with material dependent modeling.     

Vector axial-vector ambiguity in neutral currents and polarization of Δ(1236)

Measurements of the polarization density matrix in neutral current production of Δ(1236) can eliminate the vector axial-vector ambiguity for the isovector neutral couplings.     

Dissociation of acetic acid in 50 mass % ethylene carbonate-water from 20 to 55°C

The dissociation constant of acetic acid in 50 mass % ethylene carbonate-water solvents has been determined at eight temperatures from 20 to 55°C by emf measurements of cells without liquid-junction containing hydrogen electrodes and silver-silver chloride electrodes. Acetic acid is weaker in the mixed solvent than in pure water. At 25°C, pK is 5.645 as compared with 4.756 in water, in spite of the fact that the dielectric constants of the two media do not differ materially. Standard changes in Gibbs energy, enthalpy, entropy, and heat capacity for the dissociation processes at 25°C were evaluated. The decrease in acidic strength when ethylene carbonate is added to the water medium appears to be largely the results of a destabilization of the two ionic species, especially a partial desolvation of the hydrogen ion.     

Hydrogen bonding in supercritical tert-butanol assessed by vibrational spectroscopies and molecular-dynamics simulations

We have investigated the state of aggregation in supercritical tert-butanol (T = 523 K,0.05 < rho < 0.4 g cm(-3)) by means of vibrational spectroscopies (infrared and Raman) and molecular-dynamics (MD) simulations. A quantitative band shape analysis of the spectra associated with the OH stretching mode of tert-butanol has been done using activities computed by ab initio calculations on small clusters. This allows us to determine the degree of hydrogen bonding and populations of oligomers. These latter quantities have been derived from MD simulations and very consistent results are found with experiments. These results show that hydrogen bond still exist in supercritical tert-butanol and that the fluid mainly consists of oligomers smaller than tetramers.     

11H-Pyrido[3',2':4,5]pyrrolo[2,3-g]isoquinoléines (aza-7 ellipticines) substituées sur leur position 6

6-Dialkylaminoalkylamino substituted 11H-pyrido[3',2':4,5]pyrrolo[2,3-g]isoquinolines (7-aza ellipti-cines) were obtained by a six step synthesis starting from 2-chloro-3-nitro pyridine and 6-amino-5-methyl (and 5,8-dimethyl) isoquinoline-1-2H-ones already described. A brief survey of biological results shows that derivatives of this new heterocyclic ring system are less interesting than their 5H-pyrido(3',4':4,5]pyrrolo[2,3-g]isoquinolines (9-aza ellipticines) and pyrido[4,3-b]carbazoles (ellipticines) analogues.     

Influence of the polyelectrolyte molecular weight on exponentially growing multilayer films in the linear regime

Alternated deposition of polyanions and polycations on a charged solid substrate leads to the buildup of polyelectrolyte multilayer (PEM) films. Two types of PEM films were reported in the literature: films whose thickness increases linearly and films whose thickness increases exponentially with the number of deposition steps. However, it was recently found that, for exponentially growing films, the exponential increase of the film thickness takes place only during the initially deposited pairs of layers and is then followed by a linear increase. In this study, we investigate the growth process of hyaluronic acid/poly(L-lysine) (HA/PLL) and poly(L-glutamic acid)/poly(allylamine) (PGA/PAH) films, two films whose growth is initially exponential, when the growth process enters the linear regime. We focus, in particular, on the influence of the molecular weight (Mw) of the polyelectrolytes. For both systems, we find that the film thickness increment per polyanion/polycation deposition step in the linear growth regime is fairly independent of the molecular weights of the polyelectrolytes. We also find that when the (HA/PLL)n films are constructed with low molecular weight PLL, these chains can diffuse into the entire film during each buildup cycle, even for very thick films, whereas the PLL diffusion of high molecular weight chains is restricted to the upper part of the film. Our results lead to refinement of the buildup mechanism model, introduced previously for the exponentially growing films, which is based on the existence of three zones over the entire film thickness. The mechanism no longer needs all the "in" and "out" diffusing polyanions or polycations to be involved in the buildup process to explain the linear growth regime but merely relies on the interaction between the polyelectrolytes with an upper zone of the film. This zone is constituted of polyanion/polycation complexes which are "loosely bound" and rich in the polyelectrolyte deposited during the former deposition step.