Descripción: We present stopping power measurements of Zn for C and O ions and compare them with a theoretical description given by the Transport Cross Section - Extended Friedel Sum Rule (TCS-EFSR) for the valence electrons, and two different models for the inner-shells: the Shellwise Local Plasma Approximation (SLPA) and the CasP approach. The SLPA, which successfully applies to projectiles from H to B, is slightly high for C ions and clearly overestimates the data for O ions. On the other hand, total stopping results using the CasP description for the inner-shells show good agreement with the data for C and O ions, and also with the SRIM predictions. © Published under licence by IOP Publishing Ltd.

Descripción: Dielectronic recombination data for nitrogen-like ions forming oxygen-like ions has been calculated as part of the assembly of a level-resolved dielectronic recombination database necessary for the modelling of dynamic finite-density plasmas (Badnell et al. 2003). Dielectronic recombination rate coefficients for a selection of ions from O+ to Xe47+ are presented and the results discussed.

Descripción: A stationary, one-dimensional fluid model is presented to describe the interelectrode region of a nonfiltered vacuum arc operated with a background gas. The model includes the electron energy equation and the main elastic and inelastic atomic processes among metallic ions, electrons, and gas particles. To validate the model predictions an experimental study of the plasma-neutral gas structure, using a titanium (Ti) cathode and argon (Ar) as the background gas, is presented. The measured electron temperature and the experimental dependence on the pressure of neutral Ti and Ar spectroscopic emission lines are well reproduced, using a simple atomic model to interpret the plasma radiation emission. © 2006 American Institute of Physics.

Descripción: 1. 1. PBG-Deaminase obtained from Rp. palustris exhibited classical Michaelis-Menten kinetics in the absence or presence of different ions. 2. 2. Detailed kinetic studies were carried out in the presence of ammonium, phosphate and magnesium ions. 3. 3. It has been found that the different effects observed are dependent on both the substrate and the ion concentration. © 1987.

Descripción: The title compound, C 9H 14N +· CHB 11Cl 11 -, was obtained in the course of our continuing studies of the low-melting salts of closo- and nido-carborane cage anions with alkyl-pyridinium and dialkyl-imidazolium cations. The title compound is the first example of a pyridinium salt of a perchlorinated carborane anion. The structure consists of one N-butyl-pyridinium cation counterbalanced by one perchlorinated carborane cage anion per asymmetric unit. By changing the counter-ion, different packings are observed, and to try to understand this the new structure is compared with five similar compounds. © 2011 International Union of Crystallography.

Descripción: An atomistic model for Cu electrodeposition under nonequilibrium conditions is presented. Cu electrodeposition takes place with a height-dependent deposition rate that accounts for fluctuations in the local [formula presented] ions concentration at the interface, followed by surface diffusion. This model leads to an unstable interface with the development of protrusions and grooves. Subsequently the model is extended to account for the presence of organic additives, which compete with [formula presented] for adsorption at protrusions, leading to a stable interface with scaling exponents consistent with those of the Edwards-Wilkinson equation. The model reproduces the interface evolution experimentally observed for Cu electrodeposition in the absence and in the presence of organic additives. © 2002 The American Physical Society.

Descripción: Kinetic studies were carried out using purified porphobilinogenase and deaminase preparations in the presence and absence of ammonium ions. It has been found in plots of v versus [S] that a deviation from the Michaelis-Menten hyperbola occurs with both enzymes; double-reciprocal plots were concave downward; Rs values were greater than 81; and in some cases the Hill coefficient was less than 1, indicating negative homotropic kinetics. Evidence also suggested that porphobilinogenase contains at least two substrate-binding sites per molecule of enzyme. It has also been found that ammonium ions act competitively on the first reaction of the porphobilinogenase. © 1970.

Descripción: We report high magnetic field magnetostructural studies on Gd 2/3Ca1/3MnO3 single crystals. A giant linear magnetostrictive effect is observed in a wide temperature range (T < 120 K). Above 25 K a large hysteresis is seen reflecting the Mn magnetic moments ordering. At lower temperature (T < 15 K), a rather complicated field dependence arising from the competition between the Mn and Gd magnetic sublattices is observed. The relevance of the Gd ions in the low temperature behavior is further corroborated by specific heat experiments. © 2009 IOP Publishing Ltd.

Descripción: A numerical study of the space-charge sheath adjacent to the nozzle wall of a cutting torch is presented. The hydrodynamic model corresponds to a collision-dominated sheath and does not assume cold ions, so drift-diffusion-type equations are used. Also an improved expression for the ion-neutral momentum transfer is employed rather than the usual constant ion-mean-free-path or constant ion collision frequency approximations. Assuming a constant electron temperature in the sheath and neglecting the electron inertial term, the continuity and momentum equations for ions and electrons, together with Poisson's equation, were solved for the electric potential, ion velocities (both normal and tangential components), and for the ion and electron densities. It was found that both the ion and electron densities present a sudden drop at the sheath-plasma edge. The ion density continues to decrease slowly inside the sheath, while the electron density presents a virtually zero value everywhere inside the sheath, the electron thermal conduction flux to the nozzle wall being negligible. These wall results thus become thermally isolated in spite of the high electron temperature in its adjacency. For a nozzle biasing voltage close to the gas breakdown, it was found that the electric field value is high, reaching a value of about 9× 106 V m-1 at the exit of the nozzle wall. This value is higher than the average field value across the sheath and is on the order of the breakdown threshold value. This means that an undesired sheath breakdown could occur at the vicinities of the nozzle exit even if the average electric field across the sheath is not strong enough. © 2009 American Institute of Physics.

Descripción: The stacking of positively charged (or doped) terthiophene oligomers and quaterthiophene polymers in solution is investigated applying a recently developed unified electrostatic and cavitation model for first-principles calculations in a continuum solvent. The thermodynamic and structural patterns of the dimerization are explored in different solvents, and the distinctive roles of polarity and surface tension are characterized and analyzed. Interestingly, we discover a saturation in the stabilization effect of the dielectric screening that takes place at rather small values of ε0. Moreover, we address the interactions in trimers of terthiophene cations, with the aim of generalizing the results obtained for the dimers to the case of higher-order stacks and nanoaggregates. © 2006 American Institute of Physics.

Descripción: The potential energy for the diffusion of positive and negative defects in ice is calculated by a SCF-MOLCAO procedure. The resulting height of the potential energy barrier for positive defects is much lower than for negative ones, thus explaining qualitatively the greater mobility of the H 3O+ ions. It is also found that the potential-energy heights are very sensitive to the distance between the oxygens, the diffusion being greater when the oxygens are nearer. The results obtained suggest therefore that the diffusion of positive defects is correlated to the vibrations of the lattice.

Descripción: Fil:Mocskos, E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: The title compound, catena-poly[[tetrakis(μ-decanoato- κ2O:O′)-diruthenium(II, III) (Ru - Ru)]- μ-octanesulfonato-κ2O:O′], [Ru2(C10H19O2)4 (C8H17O3S)], is an octanesulfonate derivative of the mixed-valence complex diruthenium tetradecanoate. The equatorial carboxylate ligands are bidentate, bridging two Ru atoms to form a dinuclear structure. Each of the two independent dinuclear metal complexes in the asymmetric unit is located at an inversion centre. The octanesulfonate anion bridges the two dinuclear units through axial coordination. The alkyl chains of the carboxylate and sulfonate ligands are arranged in a parallel manner. The global structure can be seen as infinite chains of polar moieties separated by a double layer of non-polar alkyl groups, without interdigitation of the alkyl chains.

Descripción: Rock maenetism techniques were applied to the study of the palaeosols and loess in the Chaco-Pampean plain region, Buenos Aires, Argentina; in addition, several types of non magnetic analysis were carried out: chemical analysis of ferrous and ferric, titanium and magnesium ions and x-Ray difraction. The magnetic susceptibilities of the Argentine palaeosol and loess exhibit different trends to those observed in the well known Chinese examples with which they are compared. In the Chacopampean succession the susceptibility of the loess is higher than that of the palaeosol. This can be explained by differences in the parental material imparting different magnetic properties. © 1998 Asociaciön Geolögica Argentina.

Descripción: A programme is outlined for the assembly of a comprehensive dielectronic recombination database within the generalized collisional-radiative (GCR) framework. It is valid for modelling ions of elements in dynamic finite-density plasmas such as occur in transient astrophysical plasmas such as solar flares and in the divertors and high transport regions of magnetic fusion devices. The resolution and precision of the data are tuned to spectral analysis and so are sufficient for prediction of the dielectronic recombination contributions to individual spectral line emissivities. The fundamental data are structured according to the format prescriptions of the Atomic Data and Analysis Structure (ADAS) and the production of relevant GCR derived data for application is described and implemented following ADAS. The requirements on the dielectronic recombination database are reviewed and the new data are placed in context and evaluated with respect to older and more approximate treatments. Illustrative results validate the new high-resolution zero-density dielectronic recombination data in comparison with measurements made in heavy-ion storage rings utilizing an electron cooler. We also exemplify the role of the dielectronic data on GCR coefficient behaviour for some representative light and medium weight elements.

Descripción: 1. 1. By chromatography through Sephadex G-200 of increasing amounts of partially purified pig liver ALA-D, different profiles were obtained, showing that species of molecular weights ranging from 140,000 to 560,000 might exist in equilibrium, but their relative ratio was dependent on the total amount of protein sampled. In all cases, however, the main peak (60-70%) corresponded to the 280,000 MW oligomer, that is the octamer. 2. 2. It was found that elution profiles were also dependent on column dimensions and on the purity of the enzyme preparation. 3. 3. K+ ions affected both catalytic activity and aggregation of the enzyme. 4. Results here reported add further support to the proposal of the existence of a minimal functional dimer. © 1980.

Descripción: Measurements on the ion flux transmission in a magnetically filtered d-c vacuum arc are presented. The device includes a metallic plasma-generating chamber with water-cooled electrodes coupled to a substrate chamber through a quarter-torus magnetic filter. It is employed a Copper cathode (6 cm in diameter) with a Copper annular anode. The filter consists in a steel cylinder 500 mm length and 100 mm inner diameter with 90° of bending angle and corrugated lateral walls, surrounded by a magnetic field generating coil. The arc is operated at a current level of 100 A, and the intensity of the filtering magnetic field was in the range 0-200 G (measured at the knee of the filter). This magnetic field is enough high so as to magnetize the electrons but not the ions. The discharge is ignited by bringing (and later removing) a tungsten striker into contact with the cathode. The arc voltage drop, the floating potentials of the filter and the plasma, and the ion current collected by probes located at different positions as functions of the magnetic field intensity are reported and compared with measurements presented in the literature with other similar devices.

Descripción: A projectile ion-recoil ion and electron-recoil ion coincidence technique has been used to study the multiple ionization process in collisions of 0.75-4.0MeV B2+ with Ne atoms. Absolute total and partial pure ionization cross sections are reported for the first time at these impact energies with the present setup. The relative contribution of each recoil charge state has been investigated. The experimental data are compared to CDW-EIS calculation and with He2+ projectiles. The data throw further light on the effect of projectile screening in the ionization of multi-electronic targets and provide a support for the validity of the CDW-EIS model in this intermediate-to low velocity regime.