Determination of the Molar-Mass Averages of Random Poly(aspartate-co-lactide) Copolymers by Tuning the Ionic Strength of the Solvent

Water-soluble sodium poly(aspartate-co-lactide) (PALNa) copolymers with a molar ratio of aspartate-to-lactide units equal to 1:0.6, 1:1.0 and 1:1.5 were studied using NMR spectroscopy to determine the composition as well as SEC-MALS and static light-scattering measurements to determine the molar-mass characteristics of the copolymers. In the copolymer aqueous solutions, high-molar-mass species were detected, most probably due to the incomplete dissolution of the samples. The molar-mass averages determined in water with added simple electrolyte, i.e., NaCl, were much lower than the values determined in pure water. The concentration of the salt, which allows dissolution on a molecular level, and the separation predominantly according to a size-exclusion mechanism depend on the chemical composition of the PALNa copolymers. The optimal mobile phase for the PALNa-1/0.6 and the PALNa-1/1.0 copolymers was 0.1 M NaCl at pH 9, and for the PALNa-1/1.5 copolymer with a higher content of lactide units it was 0.05 M NaCl at pH 9. The molar-mass averages of the PALNa-1/1.0 copolymer, determined by SEC-MALS and static light-scattering measurements, were comparable.

     

Pore size distribution of micelle-templated silicas studied by thermoporosimetry using water and n-heptane

Thermoporosimetry, i.e., DSC measurements of melting point depression of water and heptane confined in mesopores, has been used for determination the pore size distribution of several mesoporous silicas synthesized with the use of micelle templates. Porosity of these materials was additionally characterized by low-temperature nitrogen adsorption and quasi-equilibrated thermodesorption of nonane. The pore size distributions obtained using the water thermoporosimetry were similar to those determined using the other methods, but the pore size values found for the narrow pore materials were underestimated by ca 1?nm. Too large pore sizes obtained for the wide pore silica from heptane thermoporosimetry were attributed to nonlinear dependence of the melting point depression on the reciprocal of the pore size.     

A non-oscillatory balanced scheme for an idealized tropical climate model

We use the non-oscillatory balanced numerical scheme developed in Part I to track the dynamics of a dry highly nonlinear barotropic/baroclinic coupled solitary wave, as introduced by Biello and Majda (2004), and of the moisture fronts of Frierson et al. (2004) in the presence of dry gravity waves, a barotropic trade wind, and the beta effect. It is demonstrated that, for the barotropic/baroclinic solitary wave, except for a little numerical dissipation, the scheme utilized here preserves total energy despite the strong interactions and exchange of energy between the baroclinic and barotropic components of the flow. After a short transient period where the numerical solution stays close to the asymptotic predictions, the flow develops small scale eddies and ultimately becomes highly turbulent. It is found here that the interaction of a dry gravity wave with a moisture front can either result in a reflection of a fast moistening front or the pure extinction of the precipitation. The barotropic trade wind stretches the precipitation patches and increases the lifetime of the moisture fronts which decay naturally by the effects of dissipation through precipitation while the Coriolis effect makes the moving precipitation patches disappear and appear at other times and places.     

Multicloud Convective Parametrizations with Crude Vertical Structure

Recent observational analysis reveals the central role of three multi-cloud types, congestus, stratiform, and deep convective cumulus clouds, in the dynamics of large scale convectively coupled Kelvin waves, westward propagating two-day waves, and the Madden–Julian oscillation. The authors have recently developed a systematic model convective parametrization highlighting the dynamic role of the three cloud types through two baroclinic modes of vertical structure: a deep convective heating mode and a second mode with low level heating and cooling corresponding respectively to congestus and stratiform clouds. The model includes a systematic moisture equation where the lower troposphere moisture increases through detrainment of shallow cumulus clouds, evaporation of stratiform rain, and moisture convergence and decreases through deep convective precipitation and a nonlinear switch which favors either deep or congestus convection depending on whether the troposphere is moist or dry. Here several new facets of these multi-cloud models are discussed including all the relevant time scales in the models and the links with simpler parametrizations involving only a single baroclinic mode in various limiting regimes. One of the new phenomena in the multi-cloud models is the existence of suitable unstable radiative convective equilibria (RCE) involving a larger fraction of congestus clouds and a smaller fraction of deep convective clouds. Novel aspects of the linear and nonlinear stability of such unstable RCE’s are studied here. They include new modes of linear instability including mesoscale second baroclinic moist gravity waves, slow moving mesoscale modes resembling squall lines, and large scale standing modes. The nonlinear instability of unstable RCE’s to homogeneous perturbations is studied with three different types of nonlinear dynamics occurring which involve adjustment to a steady deep convective RCE, periodic oscillation, and even heteroclinic chaos in suitable parameter regimes.     

A modified embedded atom method for the corundum and the bixbyite forms of alumina: Bulk and surface studies

We report an atomistic simulation study of alumina in different solid phases: the corundum and the bixbyite ones. By means of the modified embedded atom method, we show that the structural properties of bulk alumina are well reproduced compared with experimental investigations. The equilibrium energy of the bixbyite structure is found to be in the same range as the one of the corundum phase. In addition, the surface energy is also investigated for α-alumina (0 0 0 1) with both aluminum and oxygen terminations.     

Zonal Jet Creation from Secondary Instability of Drift Waves for Plasma Edge Turbulence

A new strategy is presented to explain the creation and persistence of zonal flows widely observed in plasma edge turbulence. The core physics in the edge regime of the magnetic-fusion tokamaks can be described qualitatively by the one-state modified Hasegawa-Mima (MHM for short) model, which creates enhanced zonal flows and more physically relevant features in comparison with the familiar Charney-Hasegawa-Mima (CHM for short) model for both plasma and geophysical flows. The generation mechanism of zonal jets is displayed from the secondary instability analysis via nonlinear interactions with a background base state. Strong exponential growth in the zonal modes is induced due to a non-zonal drift wave base state in the MHM model, while stabilizing damping effect is shown with a zonal flow base state. Together with the selective decay effect from the dissipation, the secondary instability offers a complete characterization of the convergence process to the purely zonal structure. Direct numerical simulations with and without dissipation are carried out to confirm the instability theory. It shows clearly the emergence of a dominant zonal flow from pure non-zonal drift waves with small perturbation in the initial configuration. In comparison, the CHM model does not create instability in the zonal modes and usually converges to homogeneous turbulence.     

Cathodic stripping determination of iron at a platinum electrode modified by adsorption of adenosine-5'-monophosphate

Irreversible adsorption of adenosine-5'-monophosphate onto platinum yields an electrode surface which is readily plated by formation of a non-labile complex with iron(III) present initially in solution or formed by oxidation of iron(II). A negative potential scan subsequent to a 60-s deposition step produces a cathodic stripping peak, the height of which is proportional to the sum of the Pe(III) and Fe(II) concentrations in solution. Oxalate can be used to mask the response to Fe(III). The method is shown to be applicable to determinations of Fe(III) and Fe(II) in the concentration range lO^-8–lO^-6 mol l^-1.     

Resonantly Interacting Weakly Nonlinear Hyperbolic Waves. I. A Single Space Variable

We present a systematic asymptotic theory for resonantly interacting weakly nonlinear hyperbolic waves in a single space variable. This theory includes as a special case the theory of nonresonant interacting waves for general hyperbolic systems developed recently by J. Hunter and J. B. Keller, when specialized to a single space variable. However, we are also able to treat the general situation when resonances occur in the hyperbolic system. Such resonances are the typical case when the hyperbolic system has at least three equations and when, for example, small-amplitude periodic initial data are prescribed. In the important physical example of the 3 × 3 system describing compressible fluid flow in a single space variable, the resonant asymptotic theory developed by the authors yields, as limit equations, a pair of inviscid Burgers equations coupled through a linear integral operator with known kernel defined through the initial data for the entropy wave. (In the general case we give many new conditions guaranteeing nonresonance for a given hyperbolic system with prescribed initial data, as well as other new structural conditions which imply that resonance occurs.) A method for treating resonantly interacting waves in several space variables, together with applications, will be developed by the authors elsewhere.